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%I #8 May 02 2020 16:15:16
%S 1,-12,1568,-445632,76844288,278739068928,-467851397312512,
%T -2679102291371999232,13369295760767407751168,
%U 198192229563606535497842688,-1400852802790123139561996419072,-65350779506647538962325382377766912
%N Expansion of cos(cos(x)-cosh(x)).
%e cos(cos(x)-cosh(x))=1-12/4!*x^4+1568/8!*x^8-445632/12!*x^12...
%t With[{nn=50},Take[CoefficientList[Series[Cos[Cos[x]-Cosh[x]],{x,0,nn}],x] Range[0,nn-2]!,{1,-1,4}]] (* _Harvey P. Dale_, May 02 2020 *)
%o (PARI) a(n)=if(n<0,0,(4*n)!*polcoeff(cos(cos(x+x*O(x^(4*n)))-cosh(x+x*O(x^(4*n)))),4*n))
%K sign,easy
%O 0,2
%A Patrick Demichel (patrick.demichel(AT)hp.com)
%E More terms from _Ralf Stephan_, Jan 17 2003