1,1

Table of n, a(n) for n=1..100.

1*(2^2)-1=3 prime so a(1)=2

7*(2^2)-1=27 composite

7*((2*3)^2)-1=251 prime so a(7)=3

Sequence in context: A328995 A036476 A104994 * A223175 A322213 A118205

Adjacent sequences: A118661 A118662 A118663 * A118665 A118666 A118667

nonn

Pierre CAMI, May 19 2006

approved