A116895 Least prime factor of n^n-1.

3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 13, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 7, 2

Offset: 2

Author

Giovanni Resta, Mar 02 2006

Keywords

• nonn

Comments

If n is odd then a(n)=2; also, if n is even and not divisible by 3 then a(n)=3. - Zak Seidov, Mar 03 2006

Examples

			6^6-1=5*7*31*43, so a(6)=5.
		

Links

• Antti Karttunen, Table of n, a(n) for n = 2..16384

Crossrefs

Cf. A006486, A007571, A048861.

Programs

Mathematica

Table[FactorInteger[GCD[n^n-1, 200! ]][[1,1]], {n, 2, 130}]

PARI

A116895(n) = { my(k=(n^n)-1); forprime(p=2, ,if(!(k%p),return(p))); }; \\ Antti Karttunen, Dec 19 2018