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 A115015 #7 May 09 2014 01:44:30
%S A115015 1,3,6,10,15,21,21,29,38,48,59,71,84,84,99,115,132,150,169,189,189,
%T A115015 211,234,258,283,309,336,336,365,395,426,458,491,525,525,561,598,636,
%U A115015 675,715,756,756,799,843,888,934,981,1029,1029,1079,1130,1182,1235,1289,1344,1344
%N A115015 Sum_{i=1..n} (gcd(7,i)=1) i.
%F A115015 a(-1-n) = a(n). - _Michael Somos_, Jul 12 2006
%o A115015 (PARI) a(n)=binomial(n+1,2)-7*binomial(n\7+1,2) /* _Michael Somos_, Jul 12 2006 */
%o A115015 (PARI) a(n)=sum(i=1,n, i*(1==gcd(7,i))) /* _Michael Somos_, Jul 12 2006 */
%Y A115015 Cf. A115012.
%K A115015 nonn
%O A115015 1,2
%A A115015 _N. J. A. Sloane_, Feb 24 2006