A167042 Squares that remain squares when prefixed with a 7.

225, 5625, 22500, 562500, 2250000, 6125625, 19580625, 56250000, 225000000, 612562500, 1958062500, 2562890625, 5625000000, 22500000000, 51472265625, 61256250000, 195806250000, 256289062500, 562500000000, 2250000000000, 5147226562500, 6125625000000

Offset: 1

Author

Claudio Meller, Oct 27 2009

Keywords

• nonn
• base

Examples

			225 = 15^2 is a square, and becomes the square 7225 = 85^2 if prefixed with a 7.
		

Links

• Chai Wah Wu, Table of n, a(n) for n = 1..1000

Programs

Mathematica

Select[Range[25*10^5]^2,IntegerQ[Sqrt[#+7*10^IntegerLength[#]]]&] (* Harvey P. Dale, Mar 02 2015 *)

Extensions

Keyword:base added by R. J. Mathar, Oct 28 2009

More terms from Chai Wah Wu, Sep 11 2014