A128887 Numbers n such that the number formed by the concatenation of the consecutive integers from 5 to n is prime.

5, 17, 71, 99, 123

Offset

1,1

Comments

Primes of this form are rare. 2 and 5 are the only beginning numbers less than 100 that form more than 2 primes for all ending numbers less than 1000.

Links

Table of n, a(n) for n=1..5.

Example

The 2nd entry forms the number 567891011121314151617 which is prime.

Prog

(PARI) consecprimes(n, m) = { local(a, x, y); a=""; for(x=m, n, a=concat(a, Str(x)); y=eval(a); if(ispseudoprime(y), print(x", "y) ) ) }

Crossrefs

Sequence in context: A249015 A273852 A146511 * A149708 A149709 A149710

Adjacent sequences: A128884 A128885 A128886 * A128888 A128889 A128890

Keyword

more,nonn,base

Author

Cino Hilliard, Apr 19 2007

Extensions

Edited by Charles R Greathouse IV, Apr 25 2010

Status

approved