A337378 - OEIS

%I #16 Dec 10 2024 11:33:11

%S 16,24,27,32,36,40,45,48,49,54,56,63,64,72,80,81,84,90,96,98,99,100,

%T 104,105,108,112,117,120,125,126,128,135,140,144,147,152,153,160,162,

%U 168,171,175,176,180,184,189,192,196,198,200,207,208,210,216,224,225,234,240,243,245,248,250,252,256,264,270,272,273

%N Numbers k for which A003961(k) > 2*sigma(k).

%C Note that A003961(n) >= sigma(n) for all n. See A286385.

%H Antti Karttunen, <a href="/A337378/b337378.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 A003961(n) = { my(f = factor(n)); for (i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); factorback(f); };

%o isA337378(n) = (A003961(n)>2*sigma(n));

%Y Subsequence of A246282 and of A337381.

%Y Positions of negative terms in A377984, and in A378751.

%Y Cf. A000203, A003961, A286385.

%Y Cf. A337379 (complement), A337380 (characteristic function).

%K nonn

%O 1,1

%A _Antti Karttunen_, Aug 27 2020