

A124121


Primes q which are the lesser of a double Wieferich prime pair. (List of known values of q in increasing order, without multiplicity.)


9




OFFSET

1,1


COMMENTS

Double Wieferich prime pairs are pairs of primes (p, q) such that q^(p1) == 1 (mod p^2) and p^(q1) == 1 (mod q^2). This sequence gives the primes q which are the lesser member (listed second) of such pairs, in increasing order, but without multiplicity:
For example, currently there are two known double Wieferich prime pairs (p, q) with q = 5: (1645333507, 5) and (188748146801, 5). In this sequence, 5 is only listed once, as a(3), and only the lesser value p=1645333507 is listed as A124122(3).
This is just the list of known pairs: there may be gaps, i.e. missing primes.


LINKS

Table of n, a(n) for n=1..6.
Yuri F. Bilu, Catalan's Conjecture, Seminaire Bourbaki, (20022003).
Michael Mossinghoff, Wieferich Prime Pairs, Barker Sequences, and Circulant Hadamard Matrices, as of Feb 12 2009.


PROG

(PARI) /* The following (highly unoptimized) code misses the value q=5 (corresponding to a very large value of p) */
default(primelimit, 1010000); forprime(q=1, default(primelimit), forprime(p=q+1, default(primelimit), Mod(p, q^2)^(q1)1 & next; Mod(q, p^2)^(p1)1  print1( q", ")  break)) \\ M. F. Hasler, Oct 08 2011


CROSSREFS

See A124122 for values of p.
Cf. A196511, A196733.
Sequence in context: A041131 A084960 A087543 * A208226 A259378 A155011
Adjacent sequences: A124118 A124119 A124120 * A124122 A124123 A124124


KEYWORD

nonn,hard,more


AUTHOR

N. J. A. Sloane, following an email from Robert G. Wilson v, Nov 30 2006


STATUS

approved



