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%I #8 Nov 28 2013 17:34:23
%S 1,2,6,6,30,5,35,35,35,70,770,770,10010,5005,15015,15015,255255,
%T 255255,4849845,4849845,1616615,3233230,74364290,74364290,74364290,
%U 37182145,37182145,37182145,1078282205,6469693230,200560490130,200560490130
%N Denominator of b(n)=sum (k'<=n,1/k') where k' denotes the squarefree numbers.
%C b(n) was used by Niven in the 1970's for an alternative proof of the divergence of the sum of reciprocals of the primes.
%H Ivan Niven, <a href="http://www.jstor.org/stable/2317524">A Proof of the Divergence of sum 1/p</a>, The American Mathematical Monthly, Vol. 78, No. 3 (Mar., 1971), pp. 272-273.
%o (PARI) a(n)=denominator(sum(k=1,n,issquarefree(k)/k))
%Y Cf. A072980.
%K easy,frac,nonn
%O 1,2
%A _Benoit Cloitre_, Aug 21 2002