1,1

All terms are primes. Note a connection to the Wieferich primes A001220(n) = {1093, 3511} = primes p such that p^2 divides 2^(p-1) - 1. a(2) = a(3) = 1093. a(3) = a(4) = 3511.

Cf. A126196, A001008 and A125581.

Cf. A126196. Cf. A125581 = numbers n such that n does not divide the denominator of the n-th harmonic number nor the denominator of the n-th alternating harmonic number. Cf. A001220 = Wieferich primes p: p^2 divides 2^(p-1) - 1. Cf. A001008, A002805 = Denominator of the n-th harmonic number. Cf. A058313, A058312 = Denominator of the n-th alternating harmonic number. Cf. A074791 = numbers n such that n does not divide the denominator of the n-th harmonic number. Cf. A121594 = numbers n such that n does not divide the denominator of the n-th alternating harmonic number.

Sequence in context: A069710 A046187 A004811 this_sequence A090814 A153435 A109217

Adjacent sequences: A126194 A126195 A126196 this_sequence A126198 A126199 A126200

nonn

Max Alekseyev and Tanya Khovanova, Mar 07 2007