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 A175634 #7 Apr 15 2021 01:18:33 %S A175634 6,9,10,15,21,22,25,33,34,35,39,49,51,55,57,58,65,69,82,85,87,91,93, %T A175634 111,115,118,119,123,129,133,141,142,145,155,159,169,177,183,187,201, %U A175634 202,205,209,213,214,215,217,219,235,237,247,249,253,259,265,267,274,287 %N A175634 Chen semiprimes: semiprimes m such that m+4 is either a prime or a semiprime. %o A175634 (Python) %o A175634 from sympy.ntheory.factor_ import primeomega, isprime %o A175634 def issemiprime(n): return primeomega(n) == 2 %o A175634 def ok(n): return issemiprime(n) and (issemiprime(n+4) or isprime(n+4)) %o A175634 print(list(filter(ok, range(1, 288)))) # _Michael S. Branicky_, Apr 14 2021 %Y A175634 Cf. A109611, A175612. %K A175634 nonn %O A175634 1,1 %A A175634 _Juri-Stepan Gerasimov_, Aug 01 2010 %E A175634 Corrected (86 replaced by 85) by _R. J. Mathar_, Aug 03 2010