1,1

nextprime(387420479) = 387420499 and (387420479+387420499)/2 = 387420489 = 3^18,

so 18 belongs to the sequence.

Cf. A115986, A115988, A115989.

Sequence in context: A119510 A137933 A143116 this_sequence A076692 A054300 A063101

Adjacent sequences: A115984 A115985 A115986 this_sequence A115988 A115989 A115990

nonn

Giovanni Resta (g.resta(AT)iit.cnr.it), Feb 10 2006