1,1

Prime p divides 3^p - 2^p - 1. 42 = 2*3*7 divides a(n) for n>2. Numbers n such that n divides 3^n - 2^n - 1 are listed in A127072(n) = {1,2,3,4,5,7,8,9,11,13,16,17,19,23,27,29,31,32,37,41,43,45,47,49,53,59,61,64,67,71,73,79,81,83,89,97,...}. Pseudoprimes in A127072(n) include all powers of primes {2,3,7} and some composite numbers that are listed in A127073(n) = {45,245,405,561,637,639,833,891,...}. Numbers n such that n^2 divides 3^n - 2^n - 1 are listed in A127074(n) = {1,2,3,4,7,49,179,619,...}. Numbers n such that n^3 divides 3^n - 2^n - 1 are {1,4,7,...}.

a(n) = (3^Prime[n] - 2^Prime[n] - 1)/Prime[n].

Table[(3^Prime[n]-2^Prime[n]-1)/Prime[n], {n, 1, 20}]

Cf. A127072, A127073, A127074.

Sequence in context: A033936 A098814 A156437 this_sequence A151333 A074015 A074021

Adjacent sequences: A127068 A127069 A127070 this_sequence A127072 A127073 A127074

nonn

Alexander Adamchuk (alex(AT)kolmogorov.com), Jan 04 2007