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 A175680 Semiprimes that are not Chen semiprimes A175634. 1
 4, 14, 26, 38, 46, 62, 74, 77, 86, 94, 95, 106, 121, 122, 134, 143, 146, 158, 161, 166, 178, 185, 194, 203, 206, 218, 221, 226, 254, 262, 278, 302, 314, 321, 326, 329, 334, 339, 341, 346, 362, 365, 371, 381, 386, 395, 398, 422, 437, 446, 451, 458, 466, 471 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Non-Chen semiprimes: semiprimes m such that m+4 is neither a prime or a semiprime. LINKS Table of n, a(n) for n=1..54. PROG (Python) from sympy.ntheory.factor_ import primeomega, isprime def issemiprime(n): return primeomega(n) == 2 def ok(n): return issemiprime(n) and not (issemiprime(n+4) or isprime(n+4)) print(list(filter(ok, range(1, 472)))) # Michael S. Branicky, Apr 14 2021 CROSSREFS Sequence in context: A080286 A075381 A030572 * A094320 A200546 A304342 Adjacent sequences: A175677 A175678 A175679 * A175681 A175682 A175683 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Aug 08 2010 EXTENSIONS Corrected (234 replaced by 254, 471 inserted) by R. J. Mathar, Aug 10 2010 STATUS approved

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Last modified May 27 02:08 EDT 2024. Contains 372847 sequences. (Running on oeis4.)