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%I #4 Aug 03 2025 16:07:33
%S 1,-1056,269568,5490816,-301315008,-6705063360,41022885888,
%T 1997915006208,25923296790720,210257663162208,1273067731422720,
%U 6245405396604288,26057761857270528,95466552284986176,314217210391363584,945049912933328640,2631525397984618944,6854687219510589888
%N Coefficients in q-expansion of E_2^2 * E_6^2, where E_2 and E_6 are respectively the Eisenstein series A006352 and A013973.
%t terms = 20;
%t E2[x_] = 1 - 24*Sum[k*x^k/(1 - x^k), {k, 1, terms}];
%t E6[x_] = 1 - 504*Sum[k^5*x^k/(1 - x^k), {k, 1, terms}];
%t CoefficientList[Series[E2[x]^2*E6[x]^2, {x, 0, 20}], x]
%Y Cf. A006352, A013973, A386787.
%K sign
%O 0,2
%A _Vaclav Kotesovec_, Aug 03 2025