A115535 Numbers k such that the concatenation of k with 4*k gives a square.

25721, 28836, 32129, 35600, 39249, 43076, 47081, 51264, 55625, 60164, 64881, 69776, 74849, 80100, 85529, 91136, 96921, 102884, 109025, 115344, 121841, 128516, 135369, 142400, 149609, 156996, 164561, 172304, 180225, 188324, 196601, 205056

Offset: 1

Author

Giovanni Resta, Jan 25 2006

Keywords

• nonn
• base

Comments

Not the same as P(n) = 89*n^2 + 2848*n + 22784: P(n) = a(n) for a < 37, but a(37) = 3698225. - Charles R Greathouse IV, Jul 28 2010

Examples

			25721_102884 = 160378^2.
		

Crossrefs

Cf. A102567, A106497, A115527 - A115556.

Programs

Mathematica

Select[Range[250000],IntegerQ[Sqrt[#*10^IntegerLength[4*#]+4*#]]&] (* Harvey P. Dale, Jan 04 2019 *)