%N Squares that remain squares when prefixed with a 5.
%C Numbers s of A000290 such that 5*10^A055642(s)+s is also in A000290.
%e 625 = 25^2 is a square and becomes the square 5625 = 75^2 if a 5 is attached in front of its decimal representation.
%p P:=proc(i) local a,n; for n from 1 by 1 to i do a:=5*10^floor(1+log10(n^2))+n^2; if a=trunc(sqrt(a))^2 then print(n^2); fi; od; end: P(1000000000000); [From _Paolo P. Lava_, Nov 02 2009]
%A _Claudio Meller_, Oct 27 2009
%E Keyword:base added by _R. J. Mathar_, Oct 28 2009