A178380 The greatest common prime divisor of n, A000032(n)-1 and A001608(n), or 1 if no such greatest common 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, 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

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