OFFSET
1,1
COMMENTS
The base-9 representation of a term 9^i + 9^j - 1 has base-9 digital sum = 1 + 8*j == 1 (mod 8).
In base-9 representation the first terms are 108, 1088, 10008, 108888, 1000088, 1008888, 1088888, 10000008, 10000888, 108888888, 10000000008, 10008888888, 10088888888, 100888888888, ...
LINKS
Hieronymus Fischer, Table of n, a(n) for n = 1..40
EXAMPLE
a(1) = 89, since 89 = 9^2 + 9^1 - 1 is prime.
a(2) = 809, since 809 = 9^3 + 9^2 - 1 is prime.
MATHEMATICA
Select[Flatten[Table[9^i+9^j-1, {i, 0, 20}, {j, 0, i-1}]], PrimeQ] (* Harvey P. Dale, Jun 02 2023 *)
PROG
CROSSREFS
KEYWORD
nonn
AUTHOR
Hieronymus Fischer, Apr 14 2014
STATUS
approved