A088276 Smallest k such that 10^k + r is a prime ending (least significant digits) in r where r is the n-th odd number not divisible by 5. 0 if no such number exists.

1, 1, 1, 1, 0, 2, 0, 3, 3, 0, 2, 0, 2, 3, 2, 2, 0, 5, 0, 2, 2, 0, 2, 0, 3, 2, 2, 3, 0, 2, 0, 2, 2, 0, 3, 0, 2, 2, 2, 2, 0, 3, 0, 3, 4, 0, 3, 0, 6, 3, 8, 3, 0, 4, 0, 4, 4, 0, 10, 0, 3, 3, 23, 4, 0, 3, 0, 4, 3, 0, 4, 0, 3, 5, 3, 5, 0, 3, 0, 6, 3, 0, 5, 0, 4, 3, 3, 633, 0, 3, 0, 3, 3, 0, 3, 0, 9, 4, 4, 3, 0, 4, 0

Offset

0,6

Comments

Conjecture: (1) The only zero entries are for values of r == 2 (mod 3). (2) There are infinitely many values of k such that 10^k + r is a prime if r is not == 2 (mod 3).

Links

Table of n, a(n) for n=0..102.

Example

The term corresponding to 21 is 3 as 21, 121 both are composite and 1021 is a prime. 1021 = 10^3 + 21 hence k = 3.

Crossrefs

Sequence in context: A200927 A258817 A004557 * A099838 A369280 A127449

Adjacent sequences: A088273 A088274 A088275 * A088277 A088278 A088279

Keyword

base,nonn

Author

Amarnath Murthy, Sep 28 2003

Extensions

More terms from Ray Chandler, Oct 15 2003

Status

approved