1,3

2*((6*1)^1) - 1 = 11 prime, so a(1)=1

2*((6*2)^1) - 1 = 23 prime, so a(2)=1

2*((6*3)^1) - 1 = 35 = 5*7

2*((6*3)^2) - 1 = 647 prime, so a(3)=2

Sequence in context: A107688 A060097 A098120 this_sequence A046876 A026584 A119326

Adjacent sequences: A098870 A098871 A098872 this_sequence A098874 A098875 A098876

nonn

Pierre CAMI (pierrecami(AT)tele2.fr), Oct 13 2004