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 A172515 #14 Apr 23 2019 02:14:00 %S A172515 3,3,4,3,3,3,4,3,3,3,4,3,3,3,4,3,3,3,4,3,3,4,3,3,3,4,3,3,3,4,3,3,3,4, %T A172515 3,3,3,4,3,3,3,4,3,3,3,4,3,3,4,3,3,3,4,3,3,3,4,3,3,3,4,3,3,3,4,3,3,3, %U A172515 4,3,3,3,4,3,3,3,4,3,3,4,3,3,3,4,3,3,3,4,3,3,3,4,3,3,3,4,3,3,3,4,3,3,3,4,3 %N A172515 First differences of A172513. %C A172515 This sequence appears to have only '3's and '4's. Indices of '4's seem to be given by A322408, but this is true only for n < 95: then the next term in A322408 is 95, but only a(96) = 4. - _M. F. Hasler_, Apr 19 2019 %o A172515 (PARI) (D(v)=v[^1]-v[^-1]); A172515_vec(N)=D(A172513_upto(N*7\2)) \\ _M. F. Hasler_, Apr 11 2019 %Y A172515 Cf. A172513, A167389. %K A172515 nonn %O A172515 1,1 %A A172515 _Stephen Crowley_, Feb 05 2010 %E A172515 Keyword "hard" removed by _M. F. Hasler_, Apr 11 2019