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A285508 Numbers with exactly three prime factors, not all distinct. 10
8, 12, 18, 20, 27, 28, 44, 45, 50, 52, 63, 68, 75, 76, 92, 98, 99, 116, 117, 124, 125, 147, 148, 153, 164, 171, 172, 175, 188, 207, 212, 236, 242, 244, 245, 261, 268, 275, 279, 284, 292, 316, 325, 332, 333, 338, 343, 356, 363, 369, 387, 388, 404, 412, 423, 425, 428, 436, 452 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Cubes of primes together with products of a prime and the square of a different prime.

Numbers n for which A001222(n) = 3, but A001221(n) < 3. - Antti Karttunen, Apr 20 2017

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

Kalle Siukola, Python program

MATHEMATICA

Select[Range[452], PrimeOmega[#] == 3 && PrimeNu[#] < 3 &] (* Giovanni Resta, Apr 20 2017 *)

PROG

(PARI)

isA285508(n) = ((omega(n) < 3) && (bigomega(n) == 3));

n=0; k=1; while(k <= 10000, n=n+1; if(isA285508(n), write("b285508.txt", k, " ", n); k=k+1));

\\ Antti Karttunen, Apr 20 2017

(Scheme, with my IntSeq-library) (define A285508 (MATCHING-POS 1 1 (lambda (n) (and (= 3 (A001222 n)) (< (A001221 n) 3))))) ;; Antti Karttunen, Apr 20 2017

(Python)

from sympy import primefactors

def omega(n): return 0 if n==1 else len(primefactors(n))

def bigomega(n): return 0 if n==1 else bigomega(n//min(primefactors(n))) + 1

print([n for n in range(1, 501) if omega(n)<3 and bigomega(n) == 3]) # Indranil Ghosh, Apr 20 2017

CROSSREFS

Cf. A001221, A001222.

Setwise difference of A014612 and A007304.

Union of A030078 and A054753.

Sequence in context: A066428 A228056 A187042 * A054397 A075818 A090738

Adjacent sequences:  A285505 A285506 A285507 * A285509 A285510 A285511

KEYWORD

easy,nonn

AUTHOR

Kalle Siukola, Apr 20 2017

STATUS

approved

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Last modified April 20 06:59 EDT 2021. Contains 343125 sequences. (Running on oeis4.)