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 A251076 #8 Feb 06 2017 18:23:23 %S A251076 1,1,1,1,1,1,1,53,141,271,449,681,973,1331,9391,26803,60953,122641, %T A251076 226921,394031,650413,2039288,5611209,13694084,30417897,62763334, %U A251076 122046063,225958222,532867801,1319078776,3196149101,7383041514,16186545853,33788903208 %N A251076 Number of tilings of a 21 X n rectangle using 3n heptominoes of shape I. %H A251076 Alois P. Heinz, <a href="/A251076/b251076.txt">Table of n, a(n) for n = 0..500</a> %H A251076 Wikipedia, <a href="https://en.wikipedia.org/wiki/Heptomino">Heptomino</a> %Y A251076 Column k=7 of A251072. %Y A251076 Cf. A250664. %K A251076 nonn %O A251076 0,8 %A A251076 _Alois P. Heinz_, Nov 29 2014