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A178380 The greatest common prime divisor of n, A000032(n)-1 and A001608(n), or 1 if no such greatest common divisor exists. 2
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, 1, 1, 1, 1, 37, 1, 1, 1, 41, 1, 43, 2, 1, 2, 47, 1, 7, 2, 1, 1, 53, 1, 1, 1, 1, 2, 59, 1, 61, 1, 1, 2, 1, 1, 67, 1, 1, 1, 71, 1, 73, 2, 1, 1, 1, 1, 79, 1, 3, 1, 83, 1, 1, 2, 1, 2, 89, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

Records of the sequence are consecutive primes.

LINKS

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

MAPLE

A000032 := proc(n) ((1+sqrt(5))/2)^n + ((1-sqrt(5))/2)^n ; expand(%) ; end proc:

A001608 := proc(n) coeftayl( (3-x^2)/(1-x^2-x^3), x=0, n) ; end proc:

A178380 := proc(n) local g; g := igcd(n, A000032(n)-1, A001608(n)) ; if g = 1 then 1; else numtheory[factorset](%) ; max( op(%)) ; end if; end proc:

seq(A178380(n), n=2..90) ; # R. J. Mathar, Aug 08 2010

CROSSREFS

Cf. A000032, A001608, A178375.

Sequence in context: A014963 A099636 A099635 * A178375 A086847 A098228

Adjacent sequences:  A178377 A178378 A178379 * A178381 A178382 A178383

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 October 30 12:22 EDT 2020. Contains 338079 sequences. (Running on oeis4.)