A065433 Numbers n such that there exist x, y with n^2 = x! + y!.

2, 5, 11, 12, 71

Offset: 1

Author

Antreas P. Hatzipolakis (xpolakis(AT)otenet.gr), Nov 23 2001

Keywords

• nonn

Comments

a(6) > 10^78. - Sascha Kurz, Mar 24 2002

a(6) > 10^1545. - Robert G. Wilson v, Apr 06 2006

a(6) > 10^10000. - Sean A. Irvine, Sep 03 2023

Examples

			2^2 = 2!+2!; 5^2 = 4!+1!; 11^2 = 5!+1!; 12^2 = 5!+4!; 71^2 = 7!+1!.
		

Links

• Lev Emelyanov, Square as sum of two factorials

Programs

Mathematica

Sqrt@ Select[ Sort@ Flatten@ Table[x! + y!, {x, 650}, {y, x}], IntegerQ@ Sqrt@ # &] (* Robert G. Wilson v, Apr 06 2006 *)