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A179858 Least positive primitive root of A139035(n). 0
3, 5, 5, 7, 3, 5, 5, 19, 3, 7, 5, 6, 17, 7, 6, 5, 3, 13, 3, 5, 7, 3, 5, 11, 5, 3, 3, 11, 5, 5, 5, 5, 6, 14, 3, 3, 3, 17, 5, 3, 3, 6, 13, 5, 7, 3, 5, 11, 5, 19, 3, 5, 5, 3, 6, 10, 5, 5, 14, 6, 3, 7, 5, 5, 7, 5, 3, 3, 11, 5, 5, 3, 5, 6, 7, 3, 5, 7, 3, 7, 5, 5, 5, 17 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

If p is a prime, then a is called a semiprimitive root if it has order (p-1)/2 and there is no x for which a^x is congruent to -1 (mod p). So +- a^k, 0 <= k <= (p-3)/2 is a complete set of nonzero residues (mod p). A primitive root has order p-1, so a number cannot be both a primitive root and a semiprimitive root.

A139035(n) are the primes for which 2 is a semiprimitive root. This sequence gives the smallest positive primitive root corresponding to each member of A139035, so each member is greater than or equal to 3.

LINKS

Table of n, a(n) for n=1..84.

EXAMPLE

Since A139035(13)=311, 2 is a semiprimitive root of 311 so j=0,...,154, {+-2^j} is a complete set of residues (congruent to {1,...,310}).  The corresponding member of this sequence is a(13)=17 because 17 is the smallest positive integer a for which {a^k}, k=0,...,309 is a complete set of residues.

MATHEMATICA

PrimitiveRoot /@ Reap[For[p = 3, p < 3000, p = NextPrime[p], rp = MultiplicativeOrder[2, p]; rm = MultiplicativeOrder[-2, p]; If[rp != p-1 && rm == p-1, Sow[p]]]][[2, 1]] (* Jean-François Alcover, Sep 03 2016, after Joerg Arndt's code for A139035 *)

CROSSREFS

Cf. A001918, A139035.

Sequence in context: A197631 A266567 A282624 * A141501 A277776 A103988

Adjacent sequences:  A179855 A179856 A179857 * A179859 A179860 A179861

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Jan 11 2011

EXTENSIONS

More terms from Jean-François Alcover, Sep 03 2016

STATUS

approved

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Last modified October 14 15:03 EDT 2019. Contains 328019 sequences. (Running on oeis4.)