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 A273357 #18 Sep 08 2022 08:46:16 %S A273357 5,25,56,89,116,209,304,401,500,601,704,809,916,1025,1316,1609,1904, %T A273357 2201,2500,2801,3104,3409,3716,4025,4336,4649,4964,5281,5600,5921, %U A273357 6244,6569,6896,7225,7556,7889,8224,8561,8900,9241,9584,9929,10681 %N A273357 Numbers n such that the decimal number concat(2,n) is a square. %C A273357 Elements are squares of integers in (sqrt(21), sqrt(30)) * sqrt(10)^k without the leading 2 elements for nonnegative k. - _David A. Corneth_, May 20 2016 %H A273357 Nathan Fox, <a href="/A273357/b273357.txt">Table of n, a(n) for n = 1..13085</a> %e A273357 56 is a member because 256 = 16^2 is a square. %e A273357 0 is not a member because 20 is not a square. %p A273357 t1:=[]; %p A273357 for k from 1 to 20000 do %p A273357 if issqr(k+2*10^length(k)) then t1:=[op(t1), k]; fi; %p A273357 od; %p A273357 t1; %o A273357 (Magma) [n: n in [1..15000 ] | IsSquare(Seqint(Intseq(n) cat Intseq(2)))]; // _Marius A. Burtea_, Mar 21 2019 %Y A273357 Cf. A272671, A273358, A273359, A273360, A273361, A273362, A273363, A273364. %K A273357 nonn,base %O A273357 1,1 %A A273357 _Nathan Fox_, _Brooke Logan_, and _N. J. A. Sloane_, May 20 2016