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 A247703 #16 Feb 06 2017 18:42:05 %S A247703 1,0,1,4,0,1,47,8,0,1,394,94,12,0,1,2082,1608,282,32,0,2,15113,8812, %T A247703 3452,512,58,0,3,111664,73863,22310,5962,790,96,0,4,789930,631700, %U A247703 218608,45762,9374,1260,142,0,5,5388729,5157928,2067811,491868,81720,15272,1824,196,0,6 %N A247703 Number T(n,k) of tilings of a 5 X n rectangle with pentominoes of any shape and exactly k pentominoes of shape I; triangle T(n,k), n>=0, 0<=k<=n, read by rows. %C A247703 Sum_{k>0} k * T(n,k) = A247736(n). %H A247703 Alois P. Heinz, <a href="/A247703/b247703.txt">Rows n = 0..140, flattened</a> %H A247703 Wikipedia, <a href="https://en.wikipedia.org/wiki/Pentomino">Pentomino</a> %e A247703 T(5,5) = 2: %e A247703 ._._._._._. ._________. %e A247703 | | | | | | |_________| %e A247703 | | | | | | |_________| %e A247703 | | | | | | |_________| %e A247703 | | | | | | |_________| %e A247703 |_|_|_|_|_| |_________| . %e A247703 Triangle T(n,k) begins: %e A247703 00 : 1; %e A247703 01 : 0, 1; %e A247703 02 : 4, 0, 1; %e A247703 03 : 47, 8, 0, 1; %e A247703 04 : 394, 94, 12, 0, 1; %e A247703 05 : 2082, 1608, 282, 32, 0, 2; %e A247703 06 : 15113, 8812, 3452, 512, 58, 0, 3; %e A247703 07 : 111664, 73863, 22310, 5962, 790, 96, 0, 4; %e A247703 08 : 789930, 631700, 218608, 45762, 9374, 1260, 142, 0, 5; %Y A247703 Row sums give A174249 or A233427(n,5). %Y A247703 Column k=0 gives A247767. %Y A247703 Main diagonal gives A003520. %Y A247703 Cf. A247736. %K A247703 nonn,tabl %O A247703 0,4 %A A247703 _Alois P. Heinz_, Sep 22 2014