Pi and By

Here’s √2 in base 2:

√2 = 1.01101010000010011110... (base=2)

And in base 3:

√2 = 1.10201122122200121221... (base=3)

And in bases 4, 5, 6, 7, 8, 9 and 10:

√2 = 1.12220021321212133303... (b=4)
√2 = 1.20134202041300003420... (b=5)
√2 = 1.22524531420552332143... (b=6)
√2 = 1.26203454521123261061... (b=7)
√2 = 1.32404746317716746220... (b=8)
√2 = 1.36485805578615303608... (b=9)
√2 = 1.41421356237309504880... (b=10)

And here’s π in the same bases:

π = 11.00100100001111110110... (b=2)
π = 10.01021101222201021100... (b=3)
π = 03.02100333122220202011... (b=4)
π = 03.03232214303343241124... (b=5)
π = 03.05033005141512410523... (b=6)
π = 03.06636514320361341102... (b=7)
π = 03.11037552421026430215... (b=8)
π = 03.12418812407442788645... (b=9)
π = 03.14159265358979323846... (b=10)

Mathematicians know that in all standard bases, the digits of √2 and π go on for ever, without falling into any regular pattern. These numbers aren’t merely irrational but transcedental. But are they also normal? That is, in each base b, do the digits 0 to [b-1] occur with the same frequency 1/b? (In general, a sequence of length l will occur in a normal number with frequency 1/(b^l).) In base 2, are there as many 1s as 0s in the digits of √2 and π? In base 3, are there as many 2s as 1s and 0s? And so on.

It’s a simple question, but so far it’s proved impossible to answer. Another question starts very simple but quickly gets very difficult. Here are the answers so far at the Online Encyclopedia of Integer Sequences (OEIS):

2, 572, 8410815, 59609420837337474 – A049364

The sequence is defined as the “Smallest number that is digitally balanced in all bases 2, 3, … n”. In base 2, the number 2 is 10, which has one 1 and one 0. In bases 2 and 3, 572 = 1000111100 and 210012, respectively. 1000111100 has five 1s and five 0s; 210012 has two 2s, two 1s and two 0s. Here are the numbers of A049364 in the necessary bases:

10 (n=2)
1000111100, 210012 (n=572)
100000000101011010111111, 120211022110200, 200011122333 (n=8410815)
11010011110001100111001111010010010001101011100110000010, 101201112000102222102011202221201100, 3103301213033102101223212002, 1000001111222333324244344 (n=59609420837337474)

But what number, a(6), satisfies the definition for bases 2, 3, 4, 5 and 6? According to the notes at the OEIS, a(6) > 5^434. That means finding a(6) is way beyond the power of present-day computers. But I assume a quantum computer could crack it. And maybe someone will come up with a short-cut or even an algorithm that supplies a(b) for any base b. Either way, I think we’ll get there, π and by.

Talcum Power

If primes are like diamonds, powers of 2 are like talc. Primes don’t crumble under division, because they can’t be divided by any number but themselves and one. Powers of 2 crumble more than any other numbers. The contrast is particularly strong when the primes are Mersenne primes, or equal to a power of 2 minus 1:

3 = 4-1 = 2^2 – 1.
4, 2, 1.

7 = 8-1 = 2^3 – 1.
8, 4, 2, 1.

31 = 32-1 = 2^5 – 1.
32, 16, 8, 4, 2, 1.

127 = 2^7 – 1.
128, 64, 32, 16, 8, 4, 2, 1.

8191 = 2^13 – 1.
8192, 4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1.

131071 = 2^17 – 1.
131072, 65536, 32768, 16384, 8192, 4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1.

524287 = 2^19 – 1.
524288, 262144, 131072, 65536, 32768, 16384, 8192, 4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1.

2147483647 = 2^31 – 1.
2147483648, 1073741824, 536870912, 268435456, 134217728, 67108864, 33554432, 16777216, 8388608, 4194304, 2097152, 1048576, 524288, 262144, 131072, 65536, 32768, 16384, 8192, 4096, 2048, 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2, 1.

Are Mersenne primes infinite? If they are, then there will be just as many Mersenne primes as powers of 2, even though very few powers of 2 create a Mersenne prime. That’s one of the paradoxes of infinity: an infinite part is equal to an infinite whole.

But are they infinite? No-one knows, though some of the greatest mathematicians in history have tried to find a proof or disproof of the conjecture. A simpler question about powers of 2 is this: Does every integer appear as part of a power of 2? I can’t find one that doesn’t:

0 is in 1024 = 2^10.
1 is in 16 = 2^4.
2 is in 32 = 2^5.
3 is in 32 = 2^5.
4 = 2^2.
5 is in 256 = 2^8.
6 is in 16 = 2^4.
7 is in 32768 = 2^15.
8 = 2^3.
9 is in 4096 = 2^12.
10 is in 1024 = 2^10.
11 is in 1099511627776 = 2^40.
12 is in 128 = 2^7.
13 is in 131072 = 2^17.
14 is in 262144 = 2^18.
15 is in 2097152 = 2^21.
16 = 2^4.
17 is in 134217728 = 2^27.
18 is in 1073741824 = 2^30.
19 is in 8192 = 2^13.
20 is in 2048 = 2^11.

666 is in 182687704666362864775460604089535377456991567872 = 2^157.
1066 is in 43556142965880123323311949751266331066368 = 2^135.
1492 is in 356811923176489970264571492362373784095686656 = 2^148.
2014 is in 3705346855594118253554271520278013051304639509300498049262642688253220148477952 = 2^261.

I’ve tested much higher than that, but testing is no good: where’s a proof? I don’t have one, though I conjecture that all integers do appear as part or whole of a power of 2. Nor do I have a proof for another conjecture: that all integers appear infinitely often as part or whole of powers of 2. Or indeed, of powers of 3, 4, 5 or any other number except powers of 10.

I conjecture that this would apply in all bases too: In any base b all n appear infinitely often as part or whole of powers of any number except those equal to a power of b.

1 is in 11 = 2^2 in base 3.
2 is in 22 = 2^3 in base 3.
10 is in 1012 = 2^5 in base 3.
11 = 2^2 in base 3.
12 is in 121 = 2^4 in base 3.
20 is in 11202 = 2^7 in base 3.
21 is in 121 = 2^4 in base 3.
22 = 2^3 in base 3.
100 is in 100111 = 2^8 in base 3.
101 is in 1012 = 2^5 in base 3.
102 is in 2210212 = 2^11 in base 3.
110 is in 1101221 = 2^10 in base 3.
111 is in 100111 = 2^8 in base 3.
112 is in 11202 = 2^7 in base 3.
120 is in 11202 = 2^7 in base 3.
121 = 2^4 in base 3.
122 is in 1101221 = 2^10 in base 3.
200 is in 200222 = 2^9 in base 3.
201 is in 12121201 = 2^12 in base 3.
202 is in 11202 = 2^7 in base 3.

1 is in 13 = 2^3 in base 5.
2 is in 112 = 2^5 in base 5.
3 is in 13 = 2^3 in base 5.
4 = 2^2 in base 5.
10 is in 1003 = 2^7 in base 5.
11 is in 112 = 2^5 in base 5.
12 is in 112 = 2^5 in base 5.
13 = 2^3 in base 5.
14 is in 31143 = 2^11 in base 5.
20 is in 2011 = 2^8 in base 5.
21 is in 4044121 = 2^16 in base 5.
22 is in 224 = 2^6 in base 5.
23 is in 112341 = 2^12 in base 5.
24 is in 224 = 2^6 in base 5.
30 is in 13044 = 2^10 in base 5.
31 = 2^4 in base 5.
32 is in 230232 = 2^13 in base 5.
33 is in 2022033 = 2^15 in base 5.
34 is in 112341 = 2^12 in base 5.
40 is in 4022 = 2^9 in base 5.

1 is in 12 = 2^3 in base 6.
2 is in 12 = 2^3 in base 6.
3 is in 332 = 2^7 in base 6.
4 = 2^2 in base 6.
5 is in 52 = 2^5 in base 6.
10 is in 1104 = 2^8 in base 6.
11 is in 1104 = 2^8 in base 6.
12 = 2^3 in base 6.
13 is in 13252 = 2^11 in base 6.
14 is in 144 = 2^6 in base 6.
15 is in 101532 = 2^13 in base 6.
20 is in 203504 = 2^14 in base 6.
21 is in 2212 = 2^9 in base 6.
22 is in 2212 = 2^9 in base 6.
23 is in 1223224 = 2^16 in base 6.
24 = 2^4 in base 6.
25 is in 13252 = 2^11 in base 6.
30 is in 30544 = 2^12 in base 6.
31 is in 15123132 = 2^19 in base 6.
32 is in 332 = 2^7 in base 6.

1 is in 11 = 2^3 in base 7.
2 is in 22 = 2^4 in base 7.
3 is in 1331 = 2^9 in base 7.
4 = 2^2 in base 7.
5 is in 514 = 2^8 in base 7.
6 is in 2662 = 2^10 in base 7.
10 is in 1054064 = 2^17 in base 7.
11 = 2^3 in base 7.
12 is in 121 = 2^6 in base 7.
13 is in 1331 = 2^9 in base 7.
14 is in 514 = 2^8 in base 7.
15 is in 35415440431 = 2^30 in base 7.
16 is in 164351 = 2^15 in base 7.
20 is in 362032 = 2^16 in base 7.
21 is in 121 = 2^6 in base 7.
22 = 2^4 in base 7.
23 is in 4312352 = 2^19 in base 7.
24 is in 242 = 2^7 in base 7.
25 is in 11625034 = 2^20 in base 7.
26 is in 2662 = 2^10 in base 7.

1 is in 17 = 2^4 in base 9.
2 is in 152 = 2^7 in base 9.
3 is in 35 = 2^5 in base 9.
4 = 2^2 in base 9.
5 is in 35 = 2^5 in base 9.
6 is in 628 = 2^9 in base 9.
7 is in 17 = 2^4 in base 9.
8 = 2^3 in base 9.
10 is in 108807 = 2^16 in base 9.
11 is in 34511011 = 2^24 in base 9.
12 is in 12212 = 2^13 in base 9.
13 is in 1357 = 2^10 in base 9.
14 is in 314 = 2^8 in base 9.
15 is in 152 = 2^7 in base 9.
16 is in 878162 = 2^19 in base 9.
17 = 2^4 in base 9.
18 is in 218715 = 2^17 in base 9.
20 is in 70122022 = 2^25 in base 9.
21 is in 12212 = 2^13 in base 9.
22 is in 12212 = 2^13 in base 9.