%I #33 Dec 10 2017 12:12:28
%S 1,5,5,17,7,41,29,77,25,43,80,197,119,281,164,127,110,501,284,639,89,
%T 791,437,963,265,1161,632,457,185,1593,860,1851,497,709,1138,2427,323,
%U 2747,1457,1029,1633,3447,1819,3831,53,1409,2219,4661,1222,5117,2675,1863
%N Denominator of the contraharmonic mean of the first n primes.
%C Is there any n > 1 for which a(n) = 1?
%C There are only two terms < 101 for n = 40..10^7: a(45)=53 and a(253)=13. - _Zak Seidov_, Dec 09 2017
%F a(n) = denominator( Sum_{k=1..n} prime(k)^2/Sum_{k=1..n} prime(k) ).
%F a(n) = denominator( A024450(n)/A007504(n) ).
%t Array[ Denominator@ ContraharmonicMean@ Prime@ Range@# &, 52] (* slightly modified by _Robert G. Wilson v_, Dec 10 2017 *)
%o (PARI) a(n) = denominator(sum(k=1, n, prime(k)^2)/sum(k=1, n, prime(k))); \\ _Michel Marcus_, Dec 01 2017
%Y Cf. A007504 (sum of the first n primes), A024450 (sum of squares of the first n primes), A296199 (numerators).
%K nonn,frac
%O 1,2
%A _Andres Cicuttin_, Nov 04 2017