A065433 - OEIS

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A065433

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

2, 5, 11, 12, 71

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

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

LINKS

Table of n, a(n) for n=1..5.

Lev Emelyanov, Square as sum of two factorials

EXAMPLE

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

MATHEMATICA

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

CROSSREFS

Sequence in context: A231336 A283473 A062889 * A032541 A363981 A281644

Adjacent sequences: A065430 A065431 A065432 * A065434 A065435 A065436

KEYWORD

nonn

AUTHOR

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

STATUS

approved