1,1

The next term is too large to include.

The terms a(1), a(2), and a(3) are primes.

The next term a(4) is a composite number, a pseudoprime to base 3.

If a(n) is a pseudoprime to base 3, then a(n+1) is a pseudoprime to base 3.

Note that a(n) divides a(n+1)-1 for every n.

a(4) has 380343 digits. - Altug Alkan, Apr 09 2016

R. Steuerwald (1948), see A005935.

Table of n, a(n) for n=1..3.

NestList[(3^# - 1)/2 &, 3, 3] (* Michael De Vlieger, Apr 06 2016 *)

Cf. A005935 (see Steuerwald's theorem), A007013, A028491.

Sequence in context: A007523 A092830 A317481 * A087345 A048756 A174211

Adjacent sequences: A271390 A271391 A271392 * A271394 A271395 A271396

nonn

Thomas Ordowski, Apr 06 2016

approved