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 A144740 #6 Jan 03 2016 15:09:20 %S A144740 0,0,0,0,1,0,2,0,1,1,4,0,4,1,2,2,6,0,6,1,2,3,8,0,6,4,6,3,10,0,10,4,5, %T A144740 5,7,2,13,6,8,4,15,1,15,6,6,7,16,2,13,5,10,8,18,3,12,7,11,11,21,1,21, %U A144740 11,11,11,15,4,23,11,14,6,24,5,24,13,11,12,18,5,26,9,17,14,27,3,19,15,19 %N A144740 Partial totient function phi(c, n) for c = 2: number of semiprimes less than and coprime to n. %C A144740 phi(c, n) = 0 iff n is in A048597. %H A144740 Reikku Kulon, <a href="/A144740/b144740.txt">Table of n, phi(2, n) for n = 1..10000</a> %e A144740 phi(2, 7) = 2: the two semiprimes less than 7 are 4 and 6. %e A144740 phi(2, 15) = 2: there are five semiprimes less than 15 (4, 6, 9, 10, 14), but only 4 and 14 are relatively prime to 15. %Y A144740 Cf. A048597. %Y A144740 Cf. A036997 (phi(n) - max(phi(c, n)) over all nonnegative integers c). %K A144740 easy,nonn %O A144740 1,7 %A A144740 _Reikku Kulon_, Sep 20 2008