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 A172181 #16 Sep 26 2015 18:39:19 %S A172181 9,15,21,27,33,35,39,45,51,57,63,65,69,75,77,81,87,93,95,99,105,111, %T A172181 117,119,123,125,129,135,141,143,147,153,155,159,161,165,171,177,183, %U A172181 185,189,195,201,203,207,209,213,215,219,221,225,231,237,243,245,249,255 %N A172181 Odd composites not of the form 6k + 1. %t A172181 Union[6Range[42] + 3, Select[6Range[43] - 1, Not[PrimeQ[#]] &]] (* _Alonso del Arte_, Jun 05 2011 *) %o A172181 (PARI) select(n->(n%6==3 && n>3) || (n%6==5 && !isprime(n)), vector(1000,i,i)) \\ _Charles R Greathouse IV_, Jun 05 2011 %Y A172181 Cf. A005408, A045375, A045410. Odd complement is A091300. %K A172181 nonn,easy %O A172181 1,1 %A A172181 _Juri-Stepan Gerasimov_, Jan 28 2010 %E A172181 Entries checked by _R. J. Mathar_, May 19 2010