1,1

If a(n) is a square, then for all k >= 1 the numbers a(n)*4^k - 1 have at least three distinct prime factors.

Table of n, a(n) for n=1..21.

Sequence in context: A022224 A230336 A252320 * A031655 A203964 A198165

Adjacent sequences: A252017 A252018 A252019 * A252021 A252022 A252023

nonn

Arkadiusz Wesolowski, Dec 15 2014

approved