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 A055617 #10 Jul 23 2013 03:52:56 %S A055617 990100,999900010000,999999000001000000,999999990000000100000000, %T A055617 999999999900000000010000000000,999999999999000000000001000000000000, %U A055617 999999999999990000000000000100000000000000 %N A055617 a(n)= A*10^(3*n)+B with A=(10^(3*n)-10^n) and B=10^(2*n). %e A055617 a(2) = (10^6-10^2)*10^6+10^4 = 999900010000. %e A055617 Note that 999900010000 = 999900^2 + 010000^2 (see A055616). %o A055617 (PARI) a(n) = (10^(3*n)-10^n)*10^(3*n) + 10^(2*n) \\ _Michel Marcus_, Jul 23 2013 %Y A055617 Subsequence of A055616. %K A055617 nonn,easy %O A055617 1,1 %A A055617 Ulrich Schimke (ulrschimke(AT)aol.com)