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

1,1

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).

Links

Table of n, a(n) for n=1..53.

Mathematica

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

Prog

(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])
(PARI) isok(n) = (bigomega(n) == 4) && (omega(n) == 2); \\ Michel Marcus, Apr 22 2019

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.

Sequence in context: A292352 A307342 A067341 * A290016 A330880 A195008

Adjacent sequences: A307679 A307680 A307681 * A307683 A307684 A307685

Keyword

nonn

Author

Kalle Siukola, Apr 21 2019

Status

approved