A112722 First n-digit number m such that sigma(m) is prime.

2, 16, 289, 1681, 10201, 146689, 1190281, 10374841, 103042801, 1023424081, 10009802401, 100019755081, 1000242014641, 10001235475729, 100001580006241, 1000017101564209, 10000044600049729, 100000569832596889

Offset

1,1

Comments

Each term is of the form p^k where p is prime. For n > 1, k is even.

Can it be proved that a(n) exists for all n?

Links

Table of n, a(n) for n=1..18.

Crossrefs

Sequence in context: A254744 A009795 A182562 * A223664 A189611 A189689

Adjacent sequences: A112719 A112720 A112721 * A112723 A112724 A112725

Keyword

nonn,base

Author

Farideh Firoozbakht, Oct 10 2005

Status

approved