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%I #8 Mar 30 2024 23:09:21
%S 1,1,17,721,58337,7734241,218014151,419784870961,153563504618177,
%T 10300599833780983,2486497854930863041,30262124466958766778001,
%U 3711710439292601861342231,26350476755161831091778460321,31166629149666821954776191205937,45673109693364177065089340171611
%N Absolute values of numerators of series expansion of cosh(x)/sqrt((cosh(x))^2+(sinh(x))^2) about 0 (even-indexed coefficients only).
%t Series[Cosh[x]/(Sqrt[Cosh[x]^2 + Sinh[x]^2]), {x, 0, 20}]
%t cc=CoefficientList[Series[Sinh[x]/(Sqrt[Cosh[x]^2+Sinh[x]^2]),{x,-,26}],x]; kk={}; Do[AppendTo[kk,Abs[Numerator[cc[[k]]]],{k,2,Length[cc],2]; kk
%Y Cf. A012085, A012193.
%K nonn
%O 0,3
%A _Artur Jasinski_, Feb 22 2007
%E Offset 0 and more terms from _Alois P. Heinz_, Apr 08 2021