A307682 Products of four primes, two of which are distinct.

24, 36, 40, 54, 56, 88, 100, 104, 135, 136, 152, 184, 189, 196, 225, 232, 248, 250, 296, 297, 328, 344, 351, 375, 376, 424, 441, 459, 472, 484, 488, 513, 536, 568, 584, 621, 632, 664, 676, 686, 712, 776, 783, 808, 824, 837, 856, 872, 875, 904, 999, 1016, 1029

Offset: 1

Author

Kalle Siukola, Apr 21 2019

Keywords

• nonn

Comments

Numbers with exactly four prime factors (counted with multiplicity) and exactly two distinct prime factors.

Numbers n such that bigomega(n) = 4 and omega(n) = 2.

Products of a prime and the cube of a different prime (pq^3) together with squares of squarefree semiprimes (p^2*q^2).

Crossrefs

Union of A065036 and A085986.

Intersection of A007774 and A067801.

Intersection of A007774 and A195086.

Intersection of A014613 and A067801.

Intersection of A014613 and A195086.

Cf. A307342.

Programs

Mathematica

Select[Range@ 1050, And[PrimeNu@ # == 2, PrimeOmega@ # == 4] &] (* Michael De Vlieger, Apr 21 2019 *)

PARI

isok(n) = (bigomega(n) == 4) && (omega(n) == 2); \\ Michel Marcus, Apr 22 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) == 2])