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 A030201 #21 Sep 06 2019 10:52:22
%S A030201 0,1,0,0,-1,0,0,-1,0,0,0,0,0,0,0,0,1,0,0,0,0,0,0,0,0,1,0,0,1,0,0,0,0,
%T A030201 0,0,0,0,-2,0,0,0,0,0,-2,0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,-1,0,
%U A030201 0,2,0,0,0,0,0,0,0,0,0,0,0,2,0
%N A030201 Expansion of eta(q^3)*eta(q^21).
%C A030201 Multiplicative. See A002655 for formula. - _Andrew Howroyd_, Aug 05 2018
%H A030201 Seiichi Manyama, <a href="/A030201/b030201.txt">Table of n, a(n) for n = 0..10000</a>
%H A030201 M. Koike, <a href="http://projecteuclid.org/euclid.nmj/1118787564">On McKay's conjecture</a>, Nagoya Math. J., 95 (1984), 85-89.
%F A030201 Expansion of x * Product_{k>=1} (1 - x^(3*k)) * (1 - x^(21*k)). - _Seiichi Manyama_, Oct 18 2016
%F A030201 a(3*n + 1) = A002655(n), a(3*n) = a(3*n + 2) = 0. - _Andrew Howroyd_, Aug 05 2018
%t A030201 q QPochhammer[q^3] QPochhammer[q^21] + O[q]^105 // CoefficientList[#, q]& (* _Jean-François Alcover_, Sep 06 2019 *)
%o A030201 (PARI) seq(n)={concat([0], Vec(eta(x^3 + O(x*x^n)) * eta(x^21 + O(x*x^n))))} \\ _Andrew Howroyd_, Aug 05 2018
%Y A030201 Expansion of eta(q^k)*eta(q^(24 - k)): A030199 (k=1), this sequence (k=3), A030213 (k=5), A030214 (k=7), A030215 (k=9), A030216 (k=10), A030217 (k=11).
%Y A030201 Cf. A002655.
%K A030201 sign,mult
%O A030201 0,38
%A A030201 _N. J. A. Sloane_