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 A049638 #11 Aug 06 2021 04:50:33 %S A049638 2,7,9,12,14,18,19,23,25,28,30,34,35,39,41,44,46,50,51,55,57,60,62,66, %T A049638 67,71,73,76,78,82,83,87,89,92,94,98,99,103,105,108,110,114,115,119, %U A049638 121,124,126,130,131,135,137,140,142,146,147,151,153,156,158,162 %N A049638 a(n) = T(n,4), array T as in A049627. %F A049638 Conjectured g.f.: 2 -x*(-7-9*x-5*x^2+2*x^3+3*x^4) / ( (1+x)*(1+x+x^2)*(x-1)^2 ). - _R. J. Mathar_, Oct 26 2015 %o A049638 (PARI) T(n,k) = (n+1)*(k+1) - sum(i=0, n, sum(j=0, k, gcd(i,j)>1)); \\ A049627 %o A049638 a(n) = T(n, 4); \\ _Michel Marcus_, Aug 06 2021 %Y A049638 Cf. A049627. %K A049638 nonn %O A049638 0,1 %A A049638 _Clark Kimberling_ %E A049638 More terms from _Sean A. Irvine_, Aug 06 2021