cp's OEIS Frontend

A113837 A number k is included if d(sigma(k)) > sigma(d(k)), where d(k) is number of positive divisors of k and sigma(k) is sum of positive divisors of k.

%I A113837 #15 Nov 14 2024 08:23:45
%S A113837 5,7,11,13,14,15,17,19,22,23,26,27,29,31,33,34,35,37,38,39,41,43,46,
%T A113837 47,51,53,54,55,56,57,58,59,61,62,65,67,69,71,73,74,77,78,79,82,83,85,
%U A113837 86,87,88,89,91,92,93,94,95,97,101,102,103,104,106,107,109,110,111,113,114
%N A113837 A number k is included if d(sigma(k)) > sigma(d(k)), where d(k) is number of positive divisors of k and sigma(k) is sum of positive divisors of k.
%e A113837 d(sigma(14)) = d(24) = 8, and sigma(d(14)) = sigma(4) = 7. Since 8 > 7, 14 is in the sequence.
%p A113837 with(numtheory): a:=proc(n) if tau(sigma(n))>sigma(tau(n)) then n else fi end: seq(a(n),n=1..122); # _Emeric Deutsch_, Feb 06 2006
%t A113837 okQ[n_] := DivisorSigma[0, DivisorSigma[1, n]] >
%t A113837            DivisorSigma[1, DivisorSigma[0, n]];
%t A113837 Select[Range[120], okQ] (* _Jean-François Alcover_, Nov 14 2024 *)
%Y A113837 Cf. A062068, A062069.
%K A113837 nonn
%O A113837 1,1
%A A113837 _Leroy Quet_, Jan 23 2006
%E A113837 More terms from _Emeric Deutsch_, Feb 06 2006