A108817 Primes of the form n*10^x + n - 1, where 0 < n < 9, x = 0,1,2,3...

3, 5, 7, 11, 13, 43, 4003, 40000003, 40000000003, 40000000000000000000000000000000000000003

Offset

1,1

Comments

The next 2 terms for x <= 1000 are 4*10^419+3 and 4*10^449+3 both PARI proved primes. Except for the first 5 terms, the outer digits of these numbers are 4 and 3. This follows from the fact that all other combinations produce multiples of 2,3 or 5.

Links

Table of n, a(n) for n=1..10.

Example

n=4,x=3. a(x,n) = 4*10^3+4-1 = 4003 prime.

Prog

(PARI) n10nm1(n) = { local(x, y, k); for(x=0, n, for(k=1, 8, y=10^x*k+k-1; if(isprime(y), print1(y", ")) ) ) }

Crossrefs

Sequence in context: A093988 A175914 A288370 * A288892 A123677 A133954

Adjacent sequences: A108814 A108815 A108816 * A108818 A108819 A108820

Keyword

nonn

Author

Cino Hilliard, Jul 11, 2005

Status

approved