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A350416
Numbers with exactly 9 semiprime divisors.
1
6300, 8820, 9900, 11700, 12600, 14700, 15300, 17100, 17640, 18900, 19404, 19800, 20700, 21780, 22050, 22932, 23400, 25200, 26100, 26460, 27900, 29400, 29700, 29988, 30420, 30492, 30600, 31500, 33300, 33516, 34200, 35100, 35280, 36300, 36900, 37800, 38700, 38808
OFFSET
1,1
COMMENTS
Numbers with exactly four distinct prime divisors (cf. A033993), one of which has multiplicity 1 and the others at least 2. - David A. Corneth, Jun 10 2022
LINKS
EXAMPLE
6300 is in the sequence as 4, 6, 9, 10, 14, 15, 21, 25, 35 are the exactly 9 of its semiprime divisors. - David A. Corneth, Jun 10 2022
MATHEMATICA
q[n_] := DivisorSum[n, 1 &, PrimeOmega[#] == 2 &] == 9; Select[Range[40000], q] (* Amiram Eldar, Dec 30 2021 *)
spd9Q[n_]:=Count[Divisors[n], _?(PrimeOmega[#]==2&)]==9; Select[Range[ 40000], spd9Q] (* Harvey P. Dale, Jun 09 2022 *)
PROG
(PARI) isok(k) = sumdiv(k, d, bigomega(d)==2) == 9; \\ Michel Marcus, Dec 30 2021
(PARI) is(n)= if(n==1, return(0)); my(f = vecsort(factor(n)[, 2])); #f == 4 && f[1] == 1 && f[2]>=2 \\ David A. Corneth, Jun 10 2022
CROSSREFS
Numbers with exactly k semiprime divisors: A346041 (k=1), A345381 (k=2), A345382 (k=3), A350371 (k=4), A350372 (k=5), A350373 (k=6), A350374 (k=7), A350375 (k=8), this sequence (k=9).
Sequence in context: A209826 A107582 A213869 * A189344 A054560 A069428
KEYWORD
nonn,easy
AUTHOR
Wesley Ivan Hurt, Dec 29 2021
STATUS
approved