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A175634 Chen semiprimes: semiprimes m such that m+4 is either a prime or a semiprime. 4
6, 9, 10, 15, 21, 22, 25, 33, 34, 35, 39, 49, 51, 55, 57, 58, 65, 69, 82, 85, 87, 91, 93, 111, 115, 118, 119, 123, 129, 133, 141, 142, 145, 155, 159, 169, 177, 183, 187, 201, 202, 205, 209, 213, 214, 215, 217, 219, 235, 237, 247, 249, 253, 259, 265, 267, 274, 287 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
PROG
(Python)
from sympy.ntheory.factor_ import primeomega, isprime
def issemiprime(n): return primeomega(n) == 2
def ok(n): return issemiprime(n) and (issemiprime(n+4) or isprime(n+4))
print(list(filter(ok, range(1, 288)))) # Michael S. Branicky, Apr 14 2021
CROSSREFS
Sequence in context: A121014 A153519 A020219 * A134622 A130593 A328234
KEYWORD
nonn
AUTHOR
EXTENSIONS
Corrected (86 replaced by 85) by R. J. Mathar, Aug 03 2010
STATUS
approved

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Last modified December 5 01:00 EST 2023. Contains 367565 sequences. (Running on oeis4.)