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 A278878 #9 Feb 06 2017 12:43:44 %S A278878 1,4,508,76003,9616962,1178422563,147382229321,18446349150367, %T A278878 2306845502243104,288660593026069762,36110872742261362007, %U A278878 4516714276347536995415,564976767651757484324113,70671912291059592748455901,8840222401663200361818980813 %N A278878 Number of tilings of a 7 X n rectangle using pentominoes of any shape and monominoes. %H A278878 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentomino">Pentomino</a> %e A278878 a(1) = 4: %e A278878 ._. ._. ._. ._. %e A278878 |_| | | |_| |_| %e A278878 |_| | | | | |_| %e A278878 |_| | | | | | | %e A278878 |_| | | | | | | %e A278878 |_| |_| | | | | %e A278878 |_| |_| |_| | | %e A278878 |_| |_| |_| |_| . %Y A278878 Column k=7 of A278657. %K A278878 nonn %O A278878 0,2 %A A278878 _Alois P. Heinz_, Nov 29 2016