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 A055619 #16 Jul 02 2023 15:45:03
%S A055619 9901009901,990099010099009901,99009900990100990099009901,
%T A055619 9900990099009901009900990099009901,
%U A055619 990099009900990099010099009900990099009901
%N A055619 a(n) = A*10^(4*n+1)+B with A=99000*(10^(4*n)-1)/9999+10 and B=9900*(10^(4*n)-1)/9999+1.
%H A055619 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (100010001, -1000100010000, 1000000000000).
%F A055619 a(n) = ( 100^(2*n+1) + 1 )^2 / 101. [_Bruno Berselli_, Jul 23 2013]
%F A055619 G.f.: 101*x*(98029801-1000000010000*x+1000000000000*x^2)/((1-x)*(1-10000*x)*(1-100000000*x)). [_Bruno Berselli_, Jul 23 2013]
%e A055619 a(2) = (99000*(10^8-1)/9999+10)*10^9+9900*(10^8-1)/9999+1 = 990099010099009901.
%e A055619 Note that 990099010099009901 = 990099010^2+099009901^2.
%t A055619 Table[(100^(2 n + 1) + 1)^2/101, {n, 5}] (* _Bruno Berselli_, Jul 23 2013 *)
%o A055619 (PARI) a(n) = (99000*(10^(4*n)-1)/9999+10)*10^(4*n+1)+9900*(10^(4*n)-1)/9999+1 \\ _Michel Marcus_, Jul 23 2013
%o A055619 (Magma) [(100^(2*n+1)+1)^2/101: n in [1..5]]; // _Bruno Berselli_, Jul 23 2013
%Y A055619 Subsequence of A055616.
%K A055619 nonn,easy
%O A055619 1,1
%A A055619 Ulrich Schimke (ulrschimke(AT)aol.com)