A125571 Least prime factor of Sum_{k=0..n-1} n^k.

3, 13, 5, 11, 7, 29, 3, 7, 11, 15797, 5, 53, 3, 11, 17, 10949, 7, 109912203092239643840221, 3, 43, 23, 461, 5, 11, 3, 109, 5, 59, 7, 568972471024107865287021434301977158534824481, 3, 67, 5, 31, 13, 149, 3, 7, 11, 83, 13, 173, 3, 19, 47

Offset: 2

Author

Axel Harvey, Jan 02 2007

Keywords

• nonn

Comments

The sequence of largest prime factors of numbers generated by the same sum is probably identical to sequence A006486, since (n^n - 1)/(1 + n^2 + ... + n^(n-1)) = n-1.

Examples

			The sum 1 + 4 + 4^2 + 4^3 = 85 = 5 * 17 so the third term is 5.
		

Links

• Chai Wah Wu, Table of n, a(n) for n = 2..178

Crossrefs

Cf. A006486.

Least prime factors of A023037.

Programs

Mathematica

Table[FactorInteger[Sum[n^k,{k,0,n-1}]][[1,1]],{n,2,46}] (* James C. McMahon, Dec 18 2024 *)

PARI

a(n) = factor(sum(k=0, n-1, n^k))[1, 1]; \\ Michel Marcus, Aug 20 2013

Extensions

More terms from Michel Marcus, Aug 20 2013