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 A342243 #40 May 01 2023 09:26:27
%S A342243 1,0,1,0,0,2,0,0,1,4,0,0,0,1,11,0,0,0,1,7,27,0,0,0,0,4,21,83,0,0,0,0,
%T A342243 2,21,91,255,0,0,0,0,1,9,89,339,847,0,0,0,0,0,6,67,393,1360,2829,0,0,
%U A342243 0,0,0,1,45,325,1713,5255,9734,0,0,0,0,0,1,23,275
%N A342243 Triangle T(n,p) read by rows: the number of n-celled polyominoes with perimeter 2p, 2 <= p <= 1+n.
%H A342243 John Mason, <a href="/A342243/b342243.txt">Table of T(n,k) for n <= 18</a> (n <= 17 from R. J. Mathar)
%H A342243 Andrew Clarke, <a href="http://www.recmath.com/PolyPages/PolyPages/index.htm?Isopolyos.html">Isoperimetrical Polyominoes</a>
%H A342243 John Mason, <a href="/A342243/a342243.csv.txt">Incomplete rows for n>18</a>
%F A342243 A131487(e) = Sum_{e=2*n+p} T(n,p).
%e A342243 The triangle has rows n=1,2,3,... and columns p=2,3,4,5,...:
%e A342243 1;
%e A342243 0, 1;
%e A342243 0, 0, 2;
%e A342243 0, 0, 1, 4;
%e A342243 0, 0, 0, 1, 11;
%e A342243 0, 0, 0, 1, 7, 27;
%e A342243 0, 0, 0, 0, 4, 21, 83;
%e A342243 0, 0, 0, 0, 2, 21, 91, 255;
%e A342243 0, 0, 0, 0, 1, 9, 89, 339, 847;
%e A342243 0, 0, 0, 0, 0, 6, 67, 393, 1360, 2829;
%e A342243 0, 0, 0, 0, 0, 1, 45, 325, 1713, 5255, 9734;
%e A342243 ...
%Y A342243 Cf. A000105 (row sums), A057730 (column sums), A131482 (diagonal), A131487 (skew antidiagonal sums), A027709 (number of leading zeros per row), A100092 (first nonzero in each row).
%K A342243 nonn,tabl,hard
%O A342243 1,6
%A A342243 _R. J. Mathar_, Mar 07 2021