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A285508 Numbers with exactly three prime factors, not all distinct. 1
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)

# Alternative program

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 xrange(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 May 29 21:28 EDT 2017. Contains 287257 sequences.