1,2

Table of n, a(n) for n=1..65.

Robert Munafo, 2^^N == 2^(2^N) mod N

3 is in the sequence because 2^2^3 = 2^8 = 256 == 1 mod 3, and 2^^3 = 2^2^2 = 2^4 = 16 == 1 mod 3.

Cf. A092188, A162018, A014221

Sequence in context: A173643 A120722 A090811 * A182764 A045880 A273011

Adjacent sequences: A161999 A162000 A162001 * A162003 A162004 A162005

easy,nonn

Robert Munafo, Jun 24 2009

approved