%I #11 Jul 15 2021 06:27:32
%S 6,28571428571428571428572,42857142857142857142858,
%T 57142857142857142857144,
%U 2247191011235955056179775280898876404494382022471910112360
%N Numbers k such that k^2 is the concatenation of two numbers m and 2*m.
%e 6^2 = 3_6.
%Y Cf. A102567, A106497, A115527 - A115556.
%K nonn,base
%O 1,1
%A _Giovanni Resta_, Jan 25 2006