[seqfan] Nice new sequence with interesting open problem

[Neil Sloane]

Sent in by Max Tohline

A326344 a(1) = 1. Thereafter, if n is prime, a(n) is the next prime after
a(n-1), but written backwards. If n is not prime, a(n) is the next
composite after a(n-1), written backwards.


1, 2, 3, 4, 5, 6, 7, 8, 9, 1, 2, 4, 5, 6, 8, 9, 11, 21, 32, 33, 43, 44, 74,
57, 85, 68, 96, 89, 79, 8, 11, 21, 22, 42, 44, 54, 95, 69, 7, 8, 11, 21,
32, 33, 43, 44, 74, 57, 85, 68, 96, 89, 79, 8, 9, 1, 4, 6, 7, 8, 11, 21,
22, 42, 44, 54, 95, 69, 7, 8, 11, 21, ...


It appears that this does not exceed 909, reached for the first time at n =
21752

Michel Marcus checked it up to 10^8.

It would be nice to know more!

The record high values are:

1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 21, 32, 33, 43, 44, 74, 85, 96, 97, 98, 99,
101, 201, 202, 302, 703, 804, 806, 807, 808, 907, 908, 909
(as far as they are known, see A326298, A326402)

Neil