A337382 - OEIS

%I #7 Aug 27 2020 17:08:42

%S 1,2,3,4,5,7,10,11,13,17,19,22,23,25,26,29,31,33,34,37,38,39,41,43,46,

%T 47,51,53,55,57,58,59,61,62,65,67,69,71,73,74,77,79,82,83,85,86,87,89,

%U 91,93,94,95,97,101,103,106,107,109,111,113,115,116,118,119,121,122,123,127,129,131,133,134,137,139,141

%N Numbers k for which A003973(k) < 2*sigma(k).

%H Antti Karttunen, <a href="/A337382/b337382.txt">Table of n, a(n) for n = 1..20000</a>

%H <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%o (PARI)

%o A003973(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); sigma(factorback(f)); };

%o isA337382(n) = (A003973(n)<2*sigma(n));

%Y Cf. A000203, A003961, A003973.

%Y Cf. A337381 (complement).

%Y Positions of zeros in A337383.

%Y Subsequence of A337379.

%Y Cf. also A246281.

%K nonn

%O 1,2

%A _Antti Karttunen_, Aug 27 2020