A273357 Numbers n such that the decimal number concat(2,n) is a square.

5, 25, 56, 89, 116, 209, 304, 401, 500, 601, 704, 809, 916, 1025, 1316, 1609, 1904, 2201, 2500, 2801, 3104, 3409, 3716, 4025, 4336, 4649, 4964, 5281, 5600, 5921, 6244, 6569, 6896, 7225, 7556, 7889, 8224, 8561, 8900, 9241, 9584, 9929, 10681

Offset: 1

Author

Nathan Fox, Brooke Logan, and N. J. A. Sloane, May 20 2016

Keywords

• nonn
• base

Comments

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

Examples

			56 is a member because 256 = 16^2 is a square.
0 is not a member because 20 is not a square.
		

Links

• Nathan Fox, Table of n, a(n) for n = 1..13085

Crossrefs

Cf. A272671, A273358, A273359, A273360, A273361, A273362, A273363, A273364.

Programs

Magma

[n: n in [1..15000 ] | IsSquare(Seqint(Intseq(n) cat Intseq(2)))]; // Marius A. Burtea, Mar 21 2019

Maple

t1:=[];
for k from 1 to 20000 do
if issqr(k+2*10^length(k)) then t1:=[op(t1), k]; fi;
od;
t1;