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%I #4 Sep 12 2016 18:22:20
%S 1,1,3,35,45045,4512611027925,2052546673789621992207225,
%T 104326219460917277964091790659689347988584942875383375,
%U 65134729714436885436168002936626505274493455112928327538888490982573786624726691153873697518277375333357875
%N Odd denominators of n * n-th harmonic number = A027611[2^n].
%C The next term (a(9)) has 218 digits. - _Harvey P. Dale_, Sep 12 2016
%F a(n) = Denominator[2^n*Sum[1/k,{k,1,2^n}]]. a(n) = A027611[2^n].
%t Denominator[Table[2^n*Sum[1/k,{k,1,2^n}],{n,0,10}]]
%t With[{nn=300},Select[Denominator[Times@@@Thread[{Range[nn],HarmonicNumber[Range[nn]]}]],OddQ]] (* _Harvey P. Dale_, Sep 12 2016 *)
%Y Cf. A027611.
%K frac,nonn
%O 0,3
%A _Alexander Adamchuk_, Jul 27 2006