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A216487 Smallest prime factor of n^(2n) - 1 having the form k*n+1. 1
3, 7, 5, 11, 7, 29, 17, 19, 11, 23, 13, 53, 29, 31, 17, 10949, 19, 108301, 41, 43, 23, 47, 73, 101, 53, 109, 29, 59, 31, 373, 257, 67, 103, 71, 37, 149, 191, 79, 41, 83, 43, 173, 89, 181, 47, 659, 97, 197, 101, 103, 53, 991313, 271, 881, 113, 4561, 349, 709 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

COMMENTS

The corresponding values of k are in A216506.

LINKS

Table of n, a(n) for n=2..59.

FORMULA

a(n) = Min{A187022(n), A187023(n)}.

EXAMPLE

a(7) = 29 because 7^14 - 1 = 2 ^ 4 * 3 * 29 * 113 * 911 * 4733 and the smallest prime divisor of the form k*n+1 is 29 = 4*7+1.

MATHEMATICA

Table[p=First/@FactorInteger[n^(2*n)-1]; Select[p, Mod[#1, n] == 1 &, 1][[1]], {n, 2, 41}]

CROSSREFS

Cf. A006486, A007571, A187022, A187023.

Sequence in context: A066677 A061026 A064632 * A328984 A328190 A090978

Adjacent sequences:  A216484 A216485 A216486 * A216488 A216489 A216490

KEYWORD

nonn

AUTHOR

Michel Lagneau, Sep 11 2012

STATUS

approved

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Last modified May 30 05:35 EDT 2020. Contains 334712 sequences. (Running on oeis4.)