On 2015-04-20 01:58, Gareth McCaughan wrote: <omitted praise for Kac monograph>
On 18/04/2015 10:16, Bill Gosper wrote:
But the cover art http://img2.imagesbn.com/p/9780883850251_p0_v1_s260x420.jpg is really stupid. --rwg
Ha. (Note in back of book: "These pictures were provided by R. William Gosper, Jr. of SYMBOLICS.")
That was back before we even had a color display, let alone a color printer. So I just sent the publisher some random color separations of Pascal's Triangle mod a couple of things. When I saw the cover, I just assumed the book designer slapped together whatever (s)he thought looked nice. But Rohan urged me to figure out what it actually was. Surprisingly, it's a coherent picture of Pascal's Triangle mod 6 (with some residues indistinguished): Graphics[Table[{EdgeForm[#], #, RegularPolygon[{4√3 (k - n/2), -6 n}, {4,π/6}, 6]} &[<|0 -> LightGray, 1 -> Red, 2 -> White, 4 -> RGBColor @@ ({74, 131, 231}/256), 3 -> Red, 5 -> Red|>@ Mod[Binomial[n, k], 6]] /. {Red ->RGBColor @@ ({250, 46, 121}/256)}, {n, 91, 161}, {k,0, n}]] Then Set Background Color to LightGray. (Not even Rohan could figure out the textual command for this.) gosper.org/kac.png --rwg