A067663 - OEIS

A067663

Sequence gives values of gcd(k!+1, k^k-1) when not equal to 1 in order of appearance.

2, 3, 5, 11, 7, 19, 11, 13, 17, 19, 43, 23, 401, 29, 31, 67, 37, 41, 43, 47, 53, 59, 61, 131, 67, 71, 73, 79, 163, 83, 89, 179, 97, 101, 103, 107, 109, 113, 227, 127, 131, 137, 139, 149, 151, 157, 163, 167, 173, 347, 179, 181, 191, 193, 197, 199, 419, 211, 443, 223

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

OFFSET

1,1

COMMENTS

Sequence appears to contain each prime number once or twice.

LINKS

Table of n, a(n) for n=1..60.

FORMULA

For some even k: gcd(k!+1, k^k-1) = k+1;

for some odd k: gcd(k!+1, k^k-1) = 2*k+1.

EXAMPLE

For k=25, gcd(k!+1, k^k-1) = 401;