login
A116895
Least prime factor of n^n-1.
3
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
2,1
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
LINKS
EXAMPLE
6^6-1=5*7*31*43, so a(6)=5.
MATHEMATICA
Table[FactorInteger[GCD[n^n-1, 200! ]][[1, 1]], {n, 2, 130}]
PROG
(PARI) A116895(n) = { my(k=(n^n)-1); forprime(p=2, , if(!(k%p), return(p))); }; \\ Antti Karttunen, Dec 19 2018
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Mar 02 2006
STATUS
approved