A108828 Primes such that the outer 2 digits are n and n+1 and all inner digits are 9, where 0 < n < 9.

293, 6997, 8999, 69997, 299993, 6999997, 89999999, 29999999993, 69999999997, 89999999999999999999, 699999999999999999997, 299999999999999999999999999993, 899999999999999999999999999999

Offset

1,1

Links

Table of n, a(n) for n=1..13.

Formula

a(x) = 10^(x+1)*n+(10^x-1)*10+n+1. Output if a(x) is prime.

Prog

(PARI) n10np9(n, d) = { local(x, y, k); for(x=1, n, for(k=1, 8, y=10^(x+1)*k+(10^x-1)*10+k+1; if(isprime(y), print1(y", ")) ) ) }

Crossrefs

Sequence in context: A342874 A241047 A085502 * A239825 A145206 A153579

Adjacent sequences: A108825 A108826 A108827 * A108829 A108830 A108831

Keyword

easy,nonn,base

Author

Cino Hilliard, Jul 11 2005

Status

approved