cp's OEIS Frontend

A376861 Numbers with a composite number of prime factors and a composite number of distinct prime factors.

%I A376861 #37 Feb 14 2025 09:56:03
%S A376861 210,330,390,462,510,546,570,690,714,770,798,840,858,870,910,930,966,
%T A376861 1110,1122,1155,1190,1218,1230,1254,1260,1290,1302,1320,1326,1330,
%U A376861 1365,1410,1430,1482,1518,1554,1560,1590,1610,1722,1770,1785,1794,1806,1830,1848,1870,1890,1914,1938,1974,1980,1995
%N A376861 Numbers with a composite number of prime factors and a composite number of distinct prime factors.
%F A376861 {k | A001221(k) in A002808 and A001222(k) in A002808}. - _Michael S. Branicky_, Feb 07 2025
%e A376861 840 is a term since 840 = 2 * 2 * 2 * 3 * 5 * 7 has 6 prime factors and 4 distinct prime factors, and both 6 and 4 are composite.
%t A376861 Select[Range[2000],CompositeQ[PrimeOmega[#]]&&CompositeQ[PrimeNu[#]]&] (* _James C. McMahon_, Feb 13 2025 *)
%o A376861 (Python)
%o A376861 from sympy import factorint, isprime
%o A376861 def ok(n):
%o A376861     f = factorint(n)
%o A376861     w, W = len(f), sum(e for e in f.values())
%o A376861     return w > 3 and W > 3 and not isprime(w) and not isprime(W)
%o A376861 print([k for k in range(1, 2000) if ok(k)]) # _Michael S. Branicky_, Feb 07 2025
%Y A376861 Cf. A001221, A001222, A002808.
%K A376861 nonn
%O A376861 1,1
%A A376861 _Marc Morgenegg_, Feb 05 2025