A337384 Numbers k for which A003973(k) is equal to 2*sigma(k).

6, 14, 15, 35, 286, 470, 715, 874, 969, 2001, 2185, 2261, 3021, 4669, 7049, 10509, 24521, 30362, 34694, 34918, 46189, 54610, 58102, 58179, 62698, 65570, 69513, 73628, 75905, 79431, 82510, 86735, 87295, 94658, 95381, 108862, 109810, 120524, 133023, 135751, 144001, 145255, 147572, 156745, 162197, 185339, 192062, 216717

Offset: 1

Author

Antti Karttunen, Aug 27 2020

Keywords

• nonn

Links

• Antti Karttunen, Table of n, a(n) for n = 1..600
• Index entries for sequences computed from indices in prime factorization
• Index entries for sequences related to sigma(n)

Crossrefs

Cf. A000203, A003961, A003973.

Subsequence of A337381.

Programs

Mathematica

Select[Range[250000], If[# == 1, 1, DivisorSigma[1, Apply[Times, FactorInteger[#] /. {p_, e_} /; e > 0 :> Prime[PrimePi@ p + 1]^e] ]] == 2 DivisorSigma[1, #] &] (* Michael De Vlieger, Aug 27 2020 *)

PARI

A003973(n) = { my(f = factor(n)); for(i=1, #f~, f[i, 1] = nextprime(f[i, 1]+1)); sigma(factorback(f)); };
isA337384(n) = (A003973(n)==2*sigma(n));