0,4

a(3)=4 because 4*2^(2^4-1)-1 = 4*2^15-1 = 4*32768-1 = 131071 which is prime.

Sequence in context: A032220 A032145 A032050 this_sequence A109915 A098987 A153017

Adjacent sequences: A057157 A057158 A057159 this_sequence A057161 A057162 A057163

nonn

Steven L. Harvey (sharvey(AT)co.coconino.az.us), Sep 14 2000