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 A122889 #10 Mar 03 2018 23:50:58
%S A122889 1,1,2,3,6,12,27,67,180,528,1676,5721,20924,81634,338322,1484209,
%T A122889 6870492,33460830,170997842,914764494,5111445917,29773148141,
%U A122889 180449216699,1136060712131,7418026238304,50163775035664
%N A122889 Antidiagonal sums of table A122888.
%C A122889 In table A122888, row n lists the coefficients of x^k, k=1..2^n, in the n-th self-composition of (x + x^2) for n>=0.
%H A122889 Paul D. Hanna, <a href="/A122889/b122889.txt">Table of n, a(n), n=0..100.</a>
%o A122889 (PARI) {a(n)=local(F=x+x^2, G, RS); RS=0; for(k=0, n, G=x+x*O(x^n); for(i=1, n-k, G=subst(F, x, G)); RS+=polcoeff(G, k, x)); RS} \\ _Paul D. Hanna_, Nov 28 2009
%Y A122889 Cf. A122888.
%K A122889 nonn
%O A122889 0,3
%A A122889 _Paul D. Hanna_, Sep 18 2006