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A350706
Composite numbers that have no "safe prime" factors.
3
4, 6, 8, 9, 12, 16, 18, 24, 26, 27, 32, 34, 36, 38, 39, 48, 51, 52, 54, 57, 58, 62, 64, 68, 72, 74, 76, 78, 81, 82, 86, 87, 93, 96, 102, 104, 106, 108, 111, 114, 116, 117, 122, 123, 124, 128, 129, 134, 136, 142, 144, 146, 148, 152, 153, 156, 158, 159, 162, 164, 169, 171
OFFSET
1,1
COMMENTS
A350705 is a subsequence.
LINKS
EXAMPLE
a(5) = 12 = 2 * 2 * 3 and {2, 3} are not in A005385.
MATHEMATICA
Select[Range[200], CompositeQ[#] && AllTrue[FactorInteger[#][[;; , 1]], ! PrimeQ[(#1 - 1)/2] &] &] (* Amiram Eldar, Feb 20 2022 *)
PROG
(PARI) isok(m) = if ((m>1) && !isprime(m), !#select(x->isprime((x-1)\2), factor(m)[, 1]));
(Python)
from sympy import primefactors, isprime
print([n for n in range(4, 172) if not isprime(n) and all(not isprime((p-1)//2) for p in primefactors(n))])
CROSSREFS
KEYWORD
nonn
AUTHOR
Karl-Heinz Hofmann, Feb 20 2022
STATUS
approved