Boustrophedon (pronounced “bough-stra-FEE-dun” or “boo-stra-FEE-dun”) is an ancient Greek word literally meaning “as the ox turns (in ploughing)”, that is, moving left-right, right-left, and so on. The word is used of writing that runs down the page in the same way. To see what that means, examine two versions of the first paragraph of Clark Ashton Smith’s story “The Demon of the Flower” (1933). The first is written in the usual way, the second is written boustrophedon:

Not as the plants and flowers of Earth, growing peacefully beneath a simple sun, were the blossoms of the planet Lophai. Coiling and uncoiling in double dawns; tossing tumultuously under vast suns of jade green and balas-ruby orange; swaying and weltering in rich twilights, in aurora-curtained nights, they resembled fields of rooted servants that dance eternally to an other-worldly music.

Not as the plants and flowers of Earth, growing peacefully

.iahpoL tenalp eht fo smossolb eht erew ,nus elpmis a htaeneb

Coiling and uncoiling in double dawns; tossing tumultuously

;egnaro ybur-salab dna neerg edaj fo snus tsav rednu

swaying and weltering in rich twilights, in aurora-curtained

ecnad taht stnavres detoor fo sdleif delbmeser yeht ,sthgin

eternally to an other-worldly music.

Boustrophedon writing was once common and sometimes the left-right lines would also be mirror-reversed, like this:

You could also use the term “boustrophedon” to describe the way this table of numbers is filled:

The table begins with “1” in the top left-hand corner, then moves right for “2”, then down for “3”, then right-and-up for “4”, “5” and “6”, then right for “7”, then left-and-down for “8”, “9” and “10”, and so on. You could also say that the numbers snake through the table. I’ve marked the primes among them, because I was interested in the patterns made by the primes when the numbers were represented as blocks on a grid, like this:

Primes are in solid white (compare the Ulam spiral). Here’s the boustrophedon prime-grid on a finer scale:

(click for full image)

And what about other number-tests? Here are the even numbers marked on the grid (i.e. n mod 2 = 0):

n mod 2 = 0

And here are some more examples of a modulus test:

n mod 3 = 0

n mod 5 = 0

n mod 9 = 0

n mod 15 = 0

n mod various = 0 (animated gif)

Next I looked at reciprocals (numbers divided into 1) marked on the grid, with the digits of a reciprocal marking the number of blank squares before a square is filled in (if the digit is “0”, the square is filled immediately). For example, in base ten 1/7 = 0.__1__42857__1__42857__1__42857…, where the block “142857” repeats for ever. When represented on the grid, 1/7 has 1 blank square, then a filled square, then 4 blank squares, then a filled square, then 2 blank squares, then a filled square, and so on:

1/7 in base 10

And here are some more reciprocals (click for full images):

1/9 in base 2

1/13 in base 10

1/27 in base 10

1/41 in base 10

1/63 in base 10

1/82 in base 10

1/101 in base 10

1/104 in base 10

1/124 in base 10

1/143 in base 10

1/175 in base 10

1/604 in base 8

1/n in various bases (animated gif)