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Semiprimes that are not Chen semiprimes A175634.
1

%I #6 Apr 14 2021 18:16:05

%S 4,14,26,38,46,62,74,77,86,94,95,106,121,122,134,143,146,158,161,166,

%T 178,185,194,203,206,218,221,226,254,262,278,302,314,321,326,329,334,

%U 339,341,346,362,365,371,381,386,395,398,422,437,446,451,458,466,471

%N Semiprimes that are not Chen semiprimes A175634.

%C Non-Chen semiprimes: semiprimes m such that m+4 is neither a prime or a semiprime.

%o (Python)

%o from sympy.ntheory.factor_ import primeomega, isprime

%o def issemiprime(n): return primeomega(n) == 2

%o def ok(n): return issemiprime(n) and not (issemiprime(n+4) or isprime(n+4))

%o print(list(filter(ok, range(1, 472)))) # _Michael S. Branicky_, Apr 14 2021

%K nonn

%O 1,1

%A _Juri-Stepan Gerasimov_, Aug 08 2010

%E Corrected (234 replaced by 254, 471 inserted) by _R. J. Mathar_, Aug 10 2010