A108818 Primes such that the outer 2 digits are n and n+1 and all inner digits are 1, where 0 < n < 9.

617, 2113, 81119, 21111113, 81111119, 8111111119, 21111111111113, 81111111111111111119, 81111111111111111111119, 2111111111111111111111113, 2111111111111111111111111111113, 611111111111111111111111111111117

Offset

1,1

Comments

The first digit of each term must be 2, 6, or 8. - Harvey P. Dale, Jun 14 2020

Links

Harvey P. Dale, Table of n, a(n) for n = 1..30

Formula

a(x) = 10^(x+1)*n+floor(10^x/9)*10+n+1. Output if a(x) is prime.

Mathematica

Select[Flatten[Table[FromDigits[Join[PadRight[{k}, n, 1], {k+1}]], {n, 2, 40}, {k, {2, 6, 8}}]], PrimeQ] (* Harvey P. Dale, Jun 14 2020 *)

Prog

(PARI) n10np1(n) = { local(x, y, k); for(x=1, n, for(k=1, 8, y=10^(x+1)*k+floor(10^x/9)*10+k+1; if(isprime(y), print1(y", ")) ) ) }

Crossrefs

Sequence in context: A275048 A350083 A275739 * A288412 A234559 A251323

Adjacent sequences: A108815 A108816 A108817 * A108819 A108820 A108821

Keyword

easy,nonn,base

Author

Cino Hilliard, Jul 11 2005

Status

approved