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 A109673 #8 Sep 08 2013 13:30:46 %S A109673 1,1,1,1,3,1,1,1,1,2,1,2,8,8,2,1,8,15,8,1,2,8,8,2,1,2,1,1,3,3,1,3,15, %T A109673 24,15,3,3,24,60,60,24,3,1,15,60,93,60,15,1,3,24,60,60,24,3,3,15,24, %U A109673 15,3,1,3,3,1,1,4,6,4,1,4,24,52,52,24,4,6,52,160,228,160,52,6,4,52 %N A109673 Hexagonal pyramid related to Prouhet-Tarry problem. %C A109673 Entries of slices [n,n] in A109672, read by rows. %C A109673 Greatest numbers in each slice (central numbers) form A002893 : 1, 3, 15, 93, 639, ... %F A109673 Sum of terms in slice [n, n] = 3^(2n); example : 1+2+1+2+8+15+8+1+2+8+8+2+1+2+1 = 3^4 = 81 for the slice [2, 2]. %e A109673 Slice [0, 0]: %e A109673 ... 1 ... %e A109673 Slice [1,1]: %e A109673 ... 1 1 ... %e A109673 .. 1 3 1 ... %e A109673 ... 1 1 ... %e A109673 Slice [2,2]: %e A109673 .... 1 2 1 ... %e A109673 ... 2 8 8 2 ... %e A109673 .. 1 8 15 8 1 ... %e A109673 ... 2 8 8 2 ... %e A109673 .... 1 2 1 .... %e A109673 Slice [3,3]: %e A109673 ...... 1 3 3 1 ..... %e A109673 .... 3 15 24 15 3 ... %e A109673 ... 3 24 60 60 24 3 ... %e A109673 .. 1 15 60 93 60 15 1 ... %e A109673 ... 3 24 60 60 24 3 ... %e A109673 .... 3 15 24 15 3 .... %e A109673 ...... 1 3 3 1 .... %K A109673 nonn,tabf,easy %O A109673 0,5 %A A109673 _Philippe Deléham_, Aug 07 2005