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A345381
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Numbers with exactly 2 semiprime divisors.
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9
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12, 18, 20, 24, 28, 40, 44, 45, 48, 50, 52, 54, 56, 63, 68, 75, 76, 80, 88, 92, 96, 98, 99, 104, 112, 116, 117, 124, 135, 136, 147, 148, 152, 153, 160, 162, 164, 171, 172, 175, 176, 184, 188, 189, 192, 207, 208, 212, 224, 232, 236, 242, 244, 245, 248, 250, 261, 268, 272, 275
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OFFSET
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1,1
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COMMENTS
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Numbers of the form p*q^k, where p and q are distinct primes and k>1.
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LINKS
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EXAMPLE
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50 is in the sequence since it has exactly 2 semiprime divisors, 10 and 25.
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MATHEMATICA
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Select[Range[300], Length[(e = Sort[FactorInteger[#][[;; , 2]]])] == 2 && Min[e] == 1 && Max[e] > 1 &] (* Amiram Eldar, Sep 30 2021 *)
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PROG
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(Python)
from sympy import factorint
def ok(n):
e = sorted(factorint(n).values())
return len(e) == 2 and e[0] == 1 and e[1] > 1
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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