A386977 - OEIS

%I #31 Aug 12 2025 18:00:45

%S 216,240,336,360,504,528,540,560,600,624,756,792,810,816,840,880,900,

%T 912,936,1000,1040,1104,1134,1176,1188,1224,1232,1260,1320,1350,1360,

%U 1368,1392,1400,1404,1456,1488,1500,1520,1560,1656,1764,1776,1782,1836,1840,1848

%N Products of 3 distinct semiprimes.

%H Alois P. Heinz, <a href="/A386977/b386977.txt">Table of n, a(n) for n = 1..10000</a>

%e 216 = 4 * 6 * 9.

%p q:= n-> (l-> l=[3$2] or nops(l)>2 and add(i, i=l)=6)(ifactors(n)[2][..., 2]):

%p select(q, [$1..2000])[];  # _Alois P. Heinz_, Aug 12 2025

%t Select[Range@ 2000, MemberQ[{{3,3}, {1,1,4}, {1,2,3}, {2,2,2}, {1,1,1,3}, {1,1,2,2}, {1,1,1,1,2}, {1,1,1,1,1,1}}, Sort[Last /@ FactorInteger@ #]] &] (* _Giovanni Resta_, Aug 12 2025 *)

%Y Cf. A001222, A001358 (semiprimes), A007304 (sphenic numbers).

%Y Subsequence of A046306.

%K nonn

%O 1,1

%A _Ian Hahus_, Aug 11 2025