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A307682 Products of four primes, two of which are distinct. 1

%I

%S 24,36,40,54,56,88,100,104,135,136,152,184,189,196,225,232,248,250,

%T 296,297,328,344,351,375,376,424,441,459,472,484,488,513,536,568,584,

%U 621,632,664,676,686,712,776,783,808,824,837,856,872,875,904,999,1016,1029

%N Products of four primes, two of which are distinct.

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

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

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

%t Select[Range@ 1050, And[PrimeNu@ # == 2, PrimeOmega@ # == 4] &] (* _Michael De Vlieger_, Apr 21 2019 *)

%o (Python 3)

%o import sympy

%o def bigomega(n): return sympy.primeomega(n)

%o def omega(n): return len(sympy.primefactors(n))

%o print([n for n in range(1, 1000) if bigomega(n) == 4 and omega(n) == 2])

%o (PARI) isok(n) = (bigomega(n) == 4) && (omega(n) == 2); \\ _Michel Marcus_, Apr 22 2019

%Y Union of A065036 and A085986.

%Y Intersection of A007774 and A067801.

%Y Intersection of A007774 and A195086.

%Y Intersection of A014613 and A067801.

%Y Intersection of A014613 and A195086.

%Y Cf. A307342.

%K nonn

%O 1,1

%A _Kalle Siukola_, Apr 21 2019

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Last modified September 18 03:39 EDT 2020. Contains 337164 sequences. (Running on oeis4.)