This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A094225 #17 Apr 30 2014 01:34:22 %S A094225 1,2,4,4,1 %N A094225 Number of distinct n-row absolute difference tables that consist entirely of the first A000217(n) natural numbers. %C A094225 Mirror image triangle pairs are consider the same. %D A094225 M. Gardner, "Pool-Ball Triangles", pp. 119-120 and 128, Penrose Tiles to Trapdoor Ciphers, Freeman NY 1989. %D A094225 M. Gardner, Puzzles From Other Worlds, Problem 8, pp. 143; 173, Random House NY 1984. %D A094225 J. D. E. Konhauser et al., " Difference triangles", Problem 145, pp. 43; 184-6, Which Way Did The Bicycle Go, MAA 1996. %D A094225 P. Tougne, " Jeux Mathematiques", Aug. 1982 issue of Pour La Science (French edition of 'Scientific American'), Paris. %H A094225 D. Greenwell, <a href="http://math2.eku.edu/greenwell/mat303/triangles/">Pool-ball Triangles</a>. %H A094225 T. Sillke, <a href="http://www.mathematik.uni-bielefeld.de/~sillke/PUZZLES/triangle-abs-diff">Absolute-difference triangles</a> %e A094225 Illustrating the case of the unique example of n=5 with numbers 1 through 15: %e A094225 6..14.15..3..13 %e A094225 ..8..1..12.10 %e A094225 ...7..11..2 %e A094225 ....4...9 %e A094225 ......5 %e A094225 For n=2 we have 1,3;2 and 2,3;1 so a(2) = 2. - _Michael Somos_, Apr 07 2012 %K A094225 nonn,fini %O A094225 1,2 %A A094225 _Lekraj Beedassy_, May 28 2004