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 A376721 #12 Oct 03 2024 09:56:51 %S A376721 1,0,0,1,1,0,1,4,1,1,9,9,2,16,36,17,26,100,101,61,226,401,274,477, %T A376721 1227,1289,1225,3186,4982,4432,7841,16040,17902,21457,45517,66610, %U A376721 71327,123444,219825,261945,354095,660573,938598,1138806,1909676,3125553 %N A376721 Expansion of 1/sqrt((1 - x^3 - x^4)^2 - 4*x^7). %F A376721 a(n) = Sum_{k=0..floor(n/3)} binomial(k,n-3*k)^2. %o A376721 (PARI) my(N=50, x='x+O('x^N)); Vec(1/sqrt((1-x^3-x^4)^2-4*x^7)) %o A376721 (PARI) a(n) = sum(k=0, n\3, binomial(k, n-3*k)^2); %Y A376721 Cf. A051286, A298567, A376722. %Y A376721 Cf. A246883. %K A376721 nonn %O A376721 0,8 %A A376721 _Seiichi Manyama_, Oct 02 2024