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A285508
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Numbers with exactly three prime factors, not all distinct.
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10
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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)
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OFFSET
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1,1
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COMMENTS
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Cubes of primes together with products of a prime and the square of a different prime.
Numbers k for which A001222(k) = 3, but A001221(k) < 3. - Antti Karttunen, Apr 20 2017
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LINKS
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Antti Karttunen, Table of n, a(n) for n = 1..10000
Kalle Siukola, Python program
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MATHEMATICA
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Select[Range[452], PrimeOmega[#] == 3 && PrimeNu[#] < 3 &] (* Giovanni Resta, Apr 20 2017 *)
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PROG
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(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
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CROSSREFS
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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
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KEYWORD
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easy,nonn
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AUTHOR
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Kalle Siukola, Apr 20 2017
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STATUS
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approved
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