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 A045826 #16 Feb 09 2018 02:12:28 %S A045826 3,4,12,0,15,12,12,0,24,12,24,0,15,16,36,0,24,24,12,0,48,12,36,0,27, %T A045826 24,36,0,24,36,36,0,48,12,48,0,24,28,48,0,51,36,24,0,72,24,24,0,24,36, %U A045826 84,0,48,36 %N A045826 a(n) = A005887(n) / 2. %H A045826 G. C. Greubel, <a href="/A045826/b045826.txt">Table of n, a(n) for n = 0..1000</a> %F A045826 Expansion of q^(-1) * (phi^3(q) - phi^3(-q)) / 4 in powers of q^2 where phi() is a Ramanujan theta function. - _Michael Somos_, Mar 12 2011 %F A045826 A005875(2*n + 1) = 2 * a(n). - _Michael Somos_, Mar 12 2011 %e A045826 3 + 4*x + 12*x^2 + 15*x^4 + 12*x^5 + 12*x^6 + 24*x^8 + 12*x^9 + ... %e A045826 3*q + 4*q^3 + 12*q^5 + 15*q^9 + 12*q^11 + 12*q^13 + 24*q^17 + 12*q^19 + ... %t A045826 A005887[n_]:= SeriesCoefficient[(EllipticTheta[3,0,q]^3 - EllipticTheta[3,0,-q]^3)/(2 q), {q, 0, n}]; Table[A005887[n]/2, {n,0, 50}][[1;; ;; 2]] (* _G. C. Greubel_, Feb 09 2018 *) %o A045826 (PARI) {a(n) = if( n<0, 0, n = 2*n + 1; polcoeff( sum( k=1, sqrtint(n), 2 * x^k^2, 1 + x*O(x^n))^3 / 2, n))} /* _Michael Somos_, Mar 12 2011 */ %Y A045826 Cf. A005875, A005887. %K A045826 nonn %O A045826 0,1 %A A045826 _N. J. A. Sloane_