1,1

Note a connection to the Wieferich primes A001220(n) = {1093, 3511} = primes p such that p^2 divides 2^(p-1) - 1. a(3) = 1093 - 1. a(4) = (3511- 1)/2. a(5) = 3511 - 1.

Cf. A126197, A001008 and A125581.

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. A126197 = GCD's arising in A126196. 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: A003396 A124899 A056852 this_sequence A093169 A159029 A068616

Adjacent sequences: A126193 A126194 A126195 this_sequence A126197 A126198 A126199

nonn

Max Alekseyev and Tanya Khovanova, Mar 07 2007, corrected Mar 10 2007