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 A049340 #17 Jul 30 2021 04:46:32 %S A049340 1,1,0,1,0,0,1,1,0,0,1,1,0,0,1,0,0,1,1,1,1,1,0,0,0,1,0,0,1,1,1,3,2,2, %T A049340 1,1,0,1,0,0,0,1,0,0,1,1,1,3,4,4,6,5,5,3,2,0,0,0,0,0,0,0,0,1,0,0,1,1, %U A049340 1,3,4,7,9,15,17,22,14,16,5,4,0,1,0,0,0 %N A049340 Triangle read by rows: T(n,k) is the number of planar graphs with n >= 1 nodes and 0 <= k <= binomial(n,2) edges, all degrees even. %H A049340 Sean A. Irvine, <a href="/A049340/b049340.txt">Table of n, a(n) for n = 1..231, rows 1..11 flattened</a> %H A049340 Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a049/A049340.java">Java program</a> (github) %e A049340 Triangle begins: %e A049340 1; %e A049340 1, 0; %e A049340 1, 0, 0, 1; %e A049340 1, 0, 0, 1, 1, 0, 0; %e A049340 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0; %e A049340 1, 0, 0, 1, 1, 1, 3, 2, 2, 1, 1, 0, 1, 0, 0, 0; %e A049340 ... %Y A049340 Rows sums give A049339. %Y A049340 Cf. A000944, A021103, A003094, A049334. %K A049340 nonn,tabf,easy,nice %O A049340 1,32 %A A049340 _Brendan McKay_ %E A049340 Entry revised by _Sean A. Irvine_, Jul 29 2021