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A346041
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Numbers with exactly 1 semiprime divisor.
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6
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4, 6, 8, 9, 10, 14, 15, 16, 21, 22, 25, 26, 27, 32, 33, 34, 35, 38, 39, 46, 49, 51, 55, 57, 58, 62, 64, 65, 69, 74, 77, 81, 82, 85, 86, 87, 91, 93, 94, 95, 106, 111, 115, 118, 119, 121, 122, 123, 125, 128, 129, 133, 134, 141, 142, 143, 145, 146, 155, 158, 159, 161, 166, 169
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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 or p^k, where p and q are prime and k >= 2.
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LINKS
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EXAMPLE
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6 is in the sequence since it has exactly 1 semiprime divisor, 6.
16 is in the sequence since it has exactly 1 semiprime divisor, 4.
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MATHEMATICA
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PROG
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(PARI) isok(k) = sumdiv(k, d, bigomega(d)==2) == 1; \\ Michel Marcus, Jul 03 2021
(Python)
from sympy import factorint
def ok(n):
f = factorint(n); w = len(f); W = sum(f.values())
return (w == 1 and W >= 2) or (w == 2 and W == 2)
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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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