A336357 - OEIS

A336357

Numbers k such that sigma(k) has fewer distinct prime factors than k.

21, 30, 42, 66, 70, 84, 93, 102, 105, 110, 138, 154, 156, 165, 170, 186, 210, 217, 230, 231, 238, 255, 273, 282, 310, 318, 322, 330, 336, 345, 357, 364, 372, 374, 381, 385, 390, 399, 400, 420, 426, 434, 462, 465, 470, 483, 506, 510, 525, 530, 546, 561, 570, 595, 630, 642, 651, 658, 660, 682, 690, 705, 710, 714

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OFFSET

1,1

COMMENTS

Numbers k for which A058062(k) < A001221(k).

If terms x and y are present and gcd(x,y) = 1, then x*y is present also.

LINKS

Table of n, a(n) for n=1..64.

MATHEMATICA

Select[Range[800], PrimeNu[#]>PrimeNu[DivisorSigma[1, #]]&] (* Harvey P. Dale, Aug 07 2021 *)

CROSSREFS

Cf. A336355 (characteristic function), A336358 (complement).