

A244550


a(n) = first odd Wieferich prime to base a(n1) for n > 1, with a(1) = 2.


5



2, 1093, 5, 20771, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71, 3, 11, 71
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OFFSET

1,1


COMMENTS

a(2) = 1093 since 1093 is the smallest odd Wieferich prime to base 2.
a(3) = 5 since 5 is the smallest odd Wieferich prime to base 1093.
Subsequence starting at a(5) is periodic with period 3, repeating the terms {3, 11, 71}.
Do values for a(1) exist such that the resulting sequence does not eventually become periodic?
The following table lists the values for a(1) and the resulting cycles those values produce. An entry of the form xy in first column means all terms from x up to and including y reach the corresponding cycle. An entry of the form {t_1, t_2, t_3, ..., t_n} in second column means the listed terms form a repeating cycle. Entries in second column without curly braces mean the listed terms are reached in order and the term following the last listed term is unknown. A question mark means no further terms have been found in the resulting trajectory of a(1).
a(1)  resulting terms

213, 1520,  {3, 11, 71}
2228, 3040, 
4246, 4859, 
6271, 7382, 
8487, 89118, 
120132, 134136,
138, 140155, 
157185, 188, 
190195, 197199 

14, 41, 60, 137,  29
196 

21, 29, 47, 61,  ?
72, 139, 186187 

83  {4871, 83}

88  2535619637, 139

119  1741

133  5277179

156  347

189  1847

Notes

The terms of the cycle reached from 83 correspond to A124121(4) and A124122(4), so those terms form a double Wieferich prime pair.


LINKS

Table of n, a(n) for n=1..70.
R. Fischer, Thema: Fermatquotient B^(P1) == 1 (mod P^2)
Index entries for linear recurrences with constant coefficients, signature (0, 0, 1).


FORMULA

From Wesley Ivan Hurt, Jun 30 2016: (Start)
G.f.: x*(2+1093*x+5*x^2+20769*x^31090*x^4+6*x^520700*x^6) / (1x^3).
a(n) = a(n3) for n>7.
a(n) = (85  52*cos(2*n*Pi/3) + 68*sqrt(3)*sin(2*n*Pi/3))/3 for n>4. (End)


MAPLE

2, 1093, 5, 20771, seq(op([3, 11, 71]), n=5..50); # Wesley Ivan Hurt, Jun 30 2016


MATHEMATICA

Join[{2, 1093, 5, 20771}, LinearRecurrence[{0, 0, 1}, {3, 11, 71}, 66]] (* Ray Chandler, Aug 25 2015 *)


PROG

(PARI) i=0; a=2; print1(a, ", "); while(i<100, forprime(p=2, 10^6, if(Mod(a, p^2)^(p1)==1 && p%2!=0, print1(p, ", "); i++; a=p; break({n=1}))))
(MAGMA) [2, 1093, 5, 20771] cat &cat [[3, 11, 71]^^30]; // Wesley Ivan Hurt, Jun 30 2016


CROSSREFS

Cf. A001220, A124121, A124122, A174422, A244546.
Sequence in context: A152510 A324590 A321633 * A039951 A247072 A282293
Adjacent sequences: A244547 A244548 A244549 * A244551 A244552 A244553


KEYWORD

nonn,easy


AUTHOR

Felix FrÃ¶hlich, Jun 29 2014


STATUS

approved



