%I #11 Nov 25 2021 12:42:34
%S 1,-3,33,-723,25953,-1376643,101031873,-9795436563,1212135593793,
%T -186388033956483,34859622790687713,-7791941518975112403,
%U 2051293521728340489633,-628173356956461494680323,221398076445213367209575553,-88980467736394156270609236243,40450409313733718675802456121473
%N a(n) = (2*n)! [x^(2*n)] cosh(x)^(-3).
%C Apparently all terms except the initial 1 have 3-valuation 1. - _F. Chapoton_, Nov 25 2021
%p egf := cosh(z)^(-3): ser := series(egf, z, 36):
%p seq((2*n)!*coeff(ser, z, 2*n), n=0..16);
%Y Row 3 of A326327.
%K sign
%O 0,2
%A _Peter Luschny_, Jul 07 2019
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