This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A175680 #6 Apr 14 2021 18:16:05 %S A175680 4,14,26,38,46,62,74,77,86,94,95,106,121,122,134,143,146,158,161,166, %T A175680 178,185,194,203,206,218,221,226,254,262,278,302,314,321,326,329,334, %U A175680 339,341,346,362,365,371,381,386,395,398,422,437,446,451,458,466,471 %N A175680 Semiprimes that are not Chen semiprimes A175634. %C A175680 Non-Chen semiprimes: semiprimes m such that m+4 is neither a prime or a semiprime. %o A175680 (Python) %o A175680 from sympy.ntheory.factor_ import primeomega, isprime %o A175680 def issemiprime(n): return primeomega(n) == 2 %o A175680 def ok(n): return issemiprime(n) and not (issemiprime(n+4) or isprime(n+4)) %o A175680 print(list(filter(ok, range(1, 472)))) # _Michael S. Branicky_, Apr 14 2021 %K A175680 nonn %O A175680 1,1 %A A175680 _Juri-Stepan Gerasimov_, Aug 08 2010 %E A175680 Corrected (234 replaced by 254, 471 inserted) by _R. J. Mathar_, Aug 10 2010