A307342 - OEIS

%I #24 Nov 13 2024 16:30:26

%S 24,36,40,54,56,60,84,88,90,100,104,126,132,135,136,140,150,152,156,

%T 184,189,196,198,204,210,220,225,228,232,234,248,250,260,276,294,296,

%U 297,306,308,315,328,330,340,342,344,348,350,351,364,372,375,376,380,390

%N Products of four primes, except fourth powers of primes.

%C Numbers with exactly four prime factors (counted with multiplicity) and more than one distinct prime factor.

%C Numbers n such that bigomega(n) = 4 and omega(n) > 1.

%t Select[Range@ 400, And[! PrimePowerQ@ #, PrimeOmega@ # == 4] &] (* _Michael De Vlieger_, Apr 21 2019 *)

%t Select[Range[400],PrimeOmega[#]==4&&PrimeNu[#]>1&] (* _Harvey P. Dale_, Aug 27 2021 *)

%o (Python)

%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) > 1])

%o (PARI) isok(n) = (bigomega(n)==4) && (omega(n) > 1); \\ _Michel Marcus_, Apr 03 2019

%Y Setwise difference of A014613 and A030514.

%Y Union of A046386, A065036, A085986 and A085987.

%Y Cf. A307682.

%K easy,nonn

%O 1,1

%A _Kalle Siukola_, Apr 02 2019