A354356 - OEIS

%I #15 May 25 2022 05:45:02

%S 1,2,3,5,6,7,10,11,14,15,17,21,22,23,30,31,33,34,35,42,46,47,51,53,55,

%T 62,66,69,70,71,77,85,93,94,102,105,106,107,110,115,119,127,138,141,

%U 142,154,155,159,161,165,170,186,187,191,210,213,214,217,230,231,235,238,253,254,255,265,282,310,318,321,322,329

%N Numbers k such that sigma(k) is 3-smooth (has no larger prime factors than 3).

%C The prime terms in this sequence are in A005105. - _Amiram Eldar_, May 25 2022

%H Amiram Eldar, <a href="/A354356/b354356.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

%t Select[Range[330], Max@ FactorInteger[DivisorSigma[1, #]][[All, 1]] <= 3 &] (* _Michael De Vlieger_, May 24 2022 *)

%o (PARI)

%o A065333(n) = ((3^valuation(n, 3)<<valuation(n, 2))==n); \\ From A065333

%o A354355(n) = A065333(sigma(n));

%o isA354356(n) = A354355(n);

%Y Cf. A000203, A065333, A354355 (characteristic function).

%Y Cf. A005105, A046528, A354357 (subsequences).

%Y Cf. also A122254.

%K nonn

%O 1,2

%A _Antti Karttunen_, May 24 2022