A307342 Products of four primes, except fourth powers of primes.

24, 36, 40, 54, 56, 60, 84, 88, 90, 100, 104, 126, 132, 135, 136, 140, 150, 152, 156, 184, 189, 196, 198, 204, 210, 220, 225, 228, 232, 234, 248, 250, 260, 276, 294, 296, 297, 306, 308, 315, 328, 330, 340, 342, 344, 348, 350, 351, 364, 372, 375, 376, 380, 390

Offset

1,1

Comments

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

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

Links

Table of n, a(n) for n=1..54.

Mathematica

Select[Range@ 400, And[! PrimePowerQ@ #, PrimeOmega@ # == 4] &] (* Michael De Vlieger, Apr 21 2019 *)
Select[Range[400], PrimeOmega[#]==4&&PrimeNu[#]>1&] (* Harvey P. Dale, Aug 27 2021 *)

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) > 1])
(PARI) isok(n) = (bigomega(n)==4) && (omega(n) > 1); \\ Michel Marcus, Apr 03 2019

Crossrefs

Setwise difference of A014613 and A030514.

Union of A046386, A065036, A085986 and A085987.

Cf. A307682.

Sequence in context: A067807 A224907 A292352 * A067341 A307682 A290016

Adjacent sequences: A307339 A307340 A307341 * A307343 A307344 A307345

Keyword

easy,nonn

Author

Kalle Siukola, Apr 02 2019

Status

approved