A087604 Smallest k such that n times concatenation of k with itself followed by a 3 is a prime, or 0 if no such number exists.

1, 1, 0, 1, 4, 0, 2, 1, 0, 1, 4, 0, 37, 7, 0, 17, 149, 0, 185, 7, 0, 73, 1, 0, 5, 47, 0, 38, 4, 0, 4, 133, 0, 52, 2, 0, 194, 46, 0, 37, 29, 0, 29, 25, 0, 19, 14, 0, 74, 8, 0, 19, 20, 0, 442, 83, 0, 358, 211, 0, 16, 298, 0, 260, 5, 0, 305, 71, 0, 8, 323, 0, 5, 109, 0, 8, 68, 0, 767, 367

Offset

1,5

Comments

Trivially a(3n) = 0. Conjecture: no other term is zero.

Either a(13)=0 or a(13)>36. This sequence contains no positive multiples of 3. If a(m) is of the form bbb...b (repeated k times) then a(km) <= b. - Sam Alexander, Oct 20 2003

Links

Table of n, a(n) for n=1..80.

Example

a(5) = 4 as 444443 is a prime. but 111113,222223,333333 are not.

Crossrefs

Cf. A086920, A087605, A087606, A087607, A087608, A087609, A087610.

Sequence in context: A324820 A346085 A337996 * A090538 A371860 A320157

Adjacent sequences: A087601 A087602 A087603 * A087605 A087606 A087607

Keyword

base,nonn

Author

Amarnath Murthy, Sep 18 2003

Extensions

More terms from Sam Alexander, Oct 20 2003

More terms from Ray G. Opao, Apr 15 2004

More terms from David Wasserman, Jun 16 2005

Status

approved