A006486 -id:A006486 - cp's OEIS frontend

A104132 Largest prime factor of pip(n)^pip(n)-1 where pip(n) is the n-th prime-indexed prime.

13, 71, 1806113, 2699538733, 568972471024107865287021434301977158534824481, 5926187589691497537793497756719

Offset: 1

Cino Hilliard, Mar 06 2005

Amiram Eldar, Table of n, a(n) for n = 1..10

Cf. A006450, A006530, A006486, A048861, A104131, A214812.

lpf[n_]:=Module[{p=Prime[Prime[n]]},FactorInteger[p^p-1][[-1,1]]]; Array[lpf,6] (* Harvey P. Dale, Nov 09 2017 *)

piptopipm1(n) = { local(x, y); for(x=1, n, y=pip(x)^pip(x)-1; print1(bdiv(y)", "); ) }
pip(n) = { return(prime(prime(n))) }
bdiv(n) = { local(x); x=ifactor(n); return(x[length(x)]) }
ifactor(n, m=0) = { local(f, j, k, flist); flist=[]; f=Vec(factor(n, m)); for(j=1, length(f[1]), for(k = 1, f[2][j], flist = concat(flist, f[1][j]) ); ); return(flist) }

a(n) = A006530(A048861(A006450(n))). - Amiram Eldar, May 23 2020

a(6) corrected by Harvey P. Dale, Nov 09 2017

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

Original entry on oeis.org

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

Axel Harvey, Jan 02 2007

nonn

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.

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

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

Cf. A006486.

Least prime factors of A023037.

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

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

More terms from Michel Marcus, Aug 20 2013

cp's OEIS Frontend

A104132 Largest prime factor of pip(n)^pip(n)-1 where pip(n) is the n-th prime-indexed prime.

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