A247229 Minimum of the greatest prime factors of (i^prime(n)-1)/(i-1), when i runs through all integers in [2, prime(n)].

3, 7, 11, 127, 89, 8191, 30839, 363889, 178481, 2089, 4404047, 616318177, 164511353, 2099863, 13264529, 20394401

Offset: 1

Author

Vladimir Shevelev, Nov 27 2014

Keywords

• nonn
• more

Comments

If in the definition "greatest" is replaced with "smallest", then we obtain A035095 (see comment there).

Crossrefs

Cf. A035095, A247216.

Programs

PARI

a(n) = {mini = 0; p = prime(n); for (i=2, p, f = factor((i^p-1)/(i-1)); gpf = f[#f~, 1]; if (! mini, mini = gpf, mini = min(mini, gpf));); mini;} \\ Michel Marcus, Dec 09 2014

Formula

a(n) == 1 (mod prime(n)).

Extensions

More terms from Peter J. C. Moses, Nov 27 2014

a(13)-a(14) from Michel Marcus, Dec 09 2014

a(15)-a(16) from Jinyuan Wang, Mar 03 2020