1,2

Near repdigit primes: concatenation of k-1 9's, one 8, and n 9's.

Pierre CAMI, Table of n, a(n) for n = 1..1100

(10^1-1)*10^1-1 = 89 prime so a(1) = 1.

(10^10-1)*10^2-1 = 999999999899 prime so a(2) = 10.

(PARI) a(n) = {my(k=1); while (!ispseudoprime(10^(n+k) - 10^n - 1), k++); k; } \\ Michel Marcus, Sep 21 2019

Sequence in context: A010180 A109013 A343102 * A240962 A324282 A085764

Adjacent sequences: A213787 A213788 A213789 * A213791 A213792 A213793

nonn

Pierre CAMI, Jun 20 2012

approved