A337399 Numbers k such that sigma(k) is a Zumkeller number (A083207).

5, 6, 11, 12, 14, 15, 19, 20, 23, 24, 26, 27, 28, 29, 33, 34, 35, 38, 39, 40, 41, 42, 44, 45, 47, 53, 54, 56, 57, 58, 59, 60, 62, 63, 65, 68, 69, 74, 76, 77, 78, 79, 80, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 95, 96, 99, 101, 102, 103

Offset

1,1

Comments

Sequence contains many semiprimes of the form p(m)*p(m+1). Only 6 of the first 200 semiprimes of this form are not terms, those where m is in {15, 37, 99, 100, 121, 197}.

Links

Amiram Eldar, Table of n, a(n) for n = 1..10000

Mathematica

zQ[n_]:=Module[{d=Divisors[n], t, ds, x}, ds=Plus@@d; If[Mod[ds, 2]>0, False, t=CoefficientList[Product[1+x^i, {i, d}], x]; t[[1+ds/2]]>0]]; Select[Range[200], zQ[DivisorSigma[1, #]]&] (* code by T. D. Noe at A083207 *)

Crossrefs

Cf. A000203, A083207, A320518 (subsequence).

Sequence in context: A287265 A120517 A246395 * A139071 A092296 A046608

Adjacent sequences: A337396 A337397 A337398 * A337400 A337401 A337402

Keyword

nonn,easy

Author

Ivan N. Ianakiev, Aug 26 2020

Status

approved