%I #7 Jul 15 2021 09:15:25
%S 1,20408163265306122448979591836734694,
%T 81632653061224489795918367346938776,
%U 20408163265306122448979591836734693877551020408163265306122448979591836734694
%N Numbers k such that the concatenation of k with 6*k gives a square.
%e 1_6 = 4^2.
%Y Cf. A102567, A106497, A115527 - A115556.
%K nonn,base,less
%O 1,2
%A _Giovanni Resta_, Jan 25 2006