A307341 Products of four primes, not all distinct.

16, 24, 36, 40, 54, 56, 60, 81, 84, 88, 90, 100, 104, 126, 132, 135, 136, 140, 150, 152, 156, 184, 189, 196, 198, 204, 220, 225, 228, 232, 234, 248, 250, 260, 276, 294, 296, 297, 306, 308, 315, 328, 340, 342, 344, 348, 350, 351, 364, 372, 375, 376, 380, 414

Offset: 1

Author

Kalle Siukola, Apr 02 2019

Keywords

• easy
• nonn

Comments

Numbers with exactly four prime factors (counted with multiplicity) but fewer than four distinct prime factors.

Numbers n such that bigomega(n) = 4 and omega(n) < 4.

Links

• Kalle Siukola, Table of n, a(n) for n = 1..10000

Crossrefs

Setwise difference of A014613 and A046386.

Union of A030514, A065036, A085986 and A085987.

Programs

PARI

isok(n) = (bigomega(n) == 4) && (omega(n) < 4); \\ Michel Marcus, Apr 03 2019

Python

import sympy
def bigomega(n): return sympy.primeomega(n)
def omega(n): return len(sympy.primefactors(n))
print([n for n in range(1, 1000) if bigomega(n) == 4 and omega(n) < 4])