A087372 Smallest k such that 3^k + 2n is a prime, or 0 if no such k exists. Index of the smallest power of 3 which when increased by the n-th even number yields a prime.

1, 1, 0, 1, 1, 0, 1, 1, 0, 1, 2, 0, 1, 1, 0, 2, 1, 0, 1, 1, 0, 1, 3, 0, 1, 2, 0, 1, 1, 0, 2, 1, 0, 1, 1, 0, 2, 1, 0, 1, 3, 0, 1, 2, 0, 2, 1, 0, 1, 1, 0, 1, 1, 0, 1, 3, 0, 4, 2, 0, 2, 1, 0, 1, 2, 0, 1, 1, 0, 2, 2, 0, 1, 1, 0, 3, 1, 0, 2, 1, 0, 1, 3, 0, 1, 2, 0, 1, 1, 0, 2, 2, 0, 1, 1, 0, 1, 1, 0, 3, 2, 0, 3, 1, 0

Offset

1,11

Comments

Most of the terms are 0, 1 or 2. Subsidiary sequence: Index of the first occurrence of n. Conjecture: There exists a finite M such that a(n) < M for all n.

Links

Table of n, a(n) for n=1..105.

Example

a(10) = 1 as 3^1 + 20 = 23 is a prime.
a(23) = 3 as 3^3 +46 = 73 is a prime but 46+3 and 46+9 are not.

Crossrefs

Cf. A087371.

Sequence in context: A140080 A345927 A065359 * A036431 A029407 A259285

Adjacent sequences: A087369 A087370 A087371 * A087373 A087374 A087375

Keyword

nonn

Author

Amarnath Murthy, Sep 09 2003

Extensions

More terms from David Wasserman, May 24 2005

Status

approved