A178375 The greatest common prime divisor of A000032(n)-1 and A001608(n), or 1 if no such divisor exists.

2, 3, 2, 5, 1, 7, 2, 3, 1, 11, 1, 13, 1, 1, 2, 17, 1, 19, 1, 1, 2, 23, 1, 5, 1, 3, 1, 29, 1, 31, 2, 7, 1, 3, 1, 37, 1, 7, 1, 41, 1, 43, 2, 1, 2, 47, 1, 7, 2, 1, 3, 53, 1, 7, 1, 1, 2, 59, 1, 61, 1, 1, 2, 7, 1, 67, 3, 1, 1, 71, 1, 73, 2, 1, 1, 5, 1, 79, 1, 7, 1, 83, 1, 2, 2, 7, 2, 89, 1

Offset

2,1

Comments

If n is prime, then n divides c(n). If n is composite and divides c(n) it is a pseudoprime to both the Lucas (Bruckman) and Perrin tests, which is the intersection of A005845 and A013998.

Conjecture: Records of the sequence are consecutive primes.

Links

Table of n, a(n) for n=2..90.

Crossrefs

Cf. A000032, A001608, A178380, A005845, A013998.

Sequence in context: A099636 A099635 A178380 * A086847 A098228 A081303

Adjacent sequences: A178372 A178373 A178374 * A178376 A178377 A178378

Keyword

nonn

Author

Vladimir Shevelev, May 26 2010

Extensions

More terms from R. J. Mathar, Aug 08 2010

Status

approved