1,1

Conjecture: 2^127 - 1 is the largest Mersenne Chen prime.

a(5)=13 because 2^13 - 1 = 8191 is prime and 2^13 + 1 = 3*2731 is semiprime.

Cf. A000043, A109611.

Sequence in context: A123856 A120857 A000043 this_sequence A109461 A138539 A090422

Adjacent sequences: A109796 A109797 A109798 this_sequence A109800 A109801 A109802

hard,more,nonn

Jason Earls (zevi_35711(AT)yahoo.com), Aug 15 2005