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 A055618 #11 Jul 02 2025 16:01:59 %S A055618 990100,99009900990100,9900990099009900990100, %T A055618 990099009900990099009900990100, %U A055618 99009900990099009900990099009900990100,9900990099009900990099009900990099009900990100,990099009900990099009900990099009900990099009900990100 %N A055618 a(n) = A*10^(4*n-1) + B with A = 990*(10^(4*n)-1)/9999 and B = 990000*(10^(4*n-4)-1)/9999 + 100. %e A055618 a(2) = (990*(10^8-1)/9999)*10^7 + 990000*(10^4-1)/9999 + 100 = 99009900990100 = 9900990^2 + 0990100^2. %p A055618 for n from 1 to 15 do printf(`%d,`,(990*(10^(4*n)-1)/9999)*10^(4*n-1)+990000*(10^(4*n-4)-1)/9999+100 ) od: %Y A055618 Subset of A055616. %K A055618 nonn,base,easy %O A055618 1,1 %A A055618 Ulrich Schimke (ulrschimke(AT)aol.com) %E A055618 One more term from _James Sellers_, Sep 28 2001 %E A055618 a(6) corrected by _Sean A. Irvine_, Mar 29 2022