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 A077431 #9 Dec 07 2019 08:19:27
%S A077431 11,22,303,404,505,606,707,8008,9009,10010,11011,12012,13013,14014,
%T A077431 15015,16016,17017,18018,19019,20020,21021,22022,230023,240024,250025,
%U A077431 260026,270027,280028,290029,300030,310031,320032,330033,340034,350035
%N A077431 n repeated in decimal representation, but separated by enough zeros that the square has the pattern (n^2)(2n^2)(n^2).
%C A077431 A077433(n) = number of separating zeros.
%F A077431 a(n) = n*(1+10^(1+floor(log_10(2*n^2)))).
%e A077431 a(17) = 17017, as 17017^2 = 289578289 = A077432(17) = 289'578'289 and 289=17^2 and 578=2*289.
%t A077431 a[n_] := For[idn = IntegerDigits[n]; k = 0, True, k++, an = FromDigits[ Join[idn, Table[0, k], idn]]; If[MatchQ[IntegerDigits[an^2], {b__ /; IntegerQ[Sqrt[FromDigits[{b}]]], c___, 0..., b__} /; FromDigits[{c}] == 2*FromDigits[{b}]], Return[an]]];
%t A077431 Array[a, 35] (* _Jean-François Alcover_, Nov 13 2017 *)
%Y A077431 Cf. A020338, A004216, A077430.
%K A077431 nonn,base
%O A077431 1,1
%A A077431 _Reinhard Zumkeller_, Nov 05 2002