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

Author

Vladimir Shevelev, May 26 2010

Keywords

• nonn

Comments

Records of the sequence are consecutive primes.

Crossrefs

Cf. A000032, A001608, A178375.

Programs

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

Extensions

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