A090270 Least positive r such that concatenation k, r, k is prime, where k == 1,3,7 or 9 (mod 10) in increasing order.

3, 1, 2, 1, 3, 3, 1, 2, 1, 6, 1, 1, 2, 5, 3, 1, 1, 5, 1, 5, 1, 3, 4, 1, 2, 4, 5, 22, 1, 6, 3, 2, 1, 3, 1, 1, 2, 4, 3, 14, 12, 15, 4, 3, 4, 1, 1, 1, 2, 14, 3, 4, 1, 3, 1, 8, 1, 4, 5, 6, 3, 4, 14, 1, 1, 5, 3, 3, 2, 6, 1, 3, 26, 2, 6, 1, 7, 2, 3, 21, 1, 3, 2, 6, 3, 2, 9, 10, 4, 3, 15, 9, 4, 7, 5, 1, 3, 5, 5, 5, 16

Offset

1,1

Links

Table of n, a(n) for n=1..101.

Example

131,313,727,919,11311,... etc. are primes.

Crossrefs

Cf. A090271.

Sequence in context: A370897 A146969 A338804 * A326441 A178830 A029329

Adjacent sequences: A090267 A090268 A090269 * A090271 A090272 A090273

Keyword

base,nonn

Author

Amarnath Murthy, Nov 28 2003

Extensions

More terms from Joshua Zucker, May 03 2006

Status

approved