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A178375 The greatest common prime divisor of A000032(n)-1 and A001608(n), or 1 of no such divisor exists. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified March 29 15:31 EDT 2017. Contains 284273 sequences.