A343216 Numbers k such that A003415(sigma(k)) < k.

1, 2, 4, 9, 13, 16, 18, 25, 36, 37, 49, 50, 61, 64, 73, 81, 97, 100, 101, 109, 113, 121, 137, 144, 157, 169, 173, 181, 193, 225, 229, 241, 242, 256, 257, 277, 281, 289, 313, 317, 324, 325, 333, 337, 353, 361, 373, 397, 400, 401, 409, 421, 433, 441, 457, 484, 512, 529, 541, 549, 576, 577, 578, 601, 613, 617, 625, 641

Offset

1,2

Links

Table of n, a(n) for n=1..68.

Index entries for sequences related to sigma(n)

Mathematica

Select[Range[641], If[#2 < 2, 0, #2 Total[#2/#1 & @@@ FactorInteger[#2]]] < #1 & @@ {#, DivisorSigma[1, #]} &] (* Michael De Vlieger, Apr 08 2021 *)

Prog

(PARI)
A003415(n) = if(n<=1, 0, my(f=factor(n)); n*sum(i=1, #f~, f[i, 2]/f[i, 1]));
isA343216(n) = (A003415(sigma(n))<n);

Crossrefs

Cf. A000203, A003415.

Cf. A343217 (complement).

Sequence in context: A266582 A376488 A227759 * A320514 A210640 A024925

Adjacent sequences: A343213 A343214 A343215 * A343217 A343218 A343219

Keyword

nonn

Author

Antti Karttunen, Apr 08 2021

Status

approved