The

set of the

factorials plus one. n!+1 for all n in

Z is prime for n={1,

2,

3,

11,

27,

37,

41,

73,

77,

116,

154,

320,

340,

399,

427,

872,

1477,

6380, ...} (these are the only ones known; the last is 21,507 digits long)

The first few numbers of this series, starting with n=1, are 2, 3, 7, 25, 121, 721, 5041, 40321, 362881, 3628801, 39916801 ...