1,1

First unknown: 361.

Table of n, a(n) for n=1..8.

a(4) = 13 so 1234567891234 = 2 * 617283945617 is a semiprime.

Cf. A057137.

Sequence in context: A280224 A282718 A092406 * A254310 A121174 A050071

Adjacent sequences: A250294 A250295 A250296 * A250298 A250299 A250300

nonn,base

Eric Chen, Dec 26 2014

approved