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A047389 Numbers that are congruent to {3, 5} mod 7. 5
3, 5, 10, 12, 17, 19, 24, 26, 31, 33, 38, 40, 45, 47, 52, 54, 59, 61, 66, 68, 73, 75, 80, 82, 87, 89, 94, 96, 101, 103, 108, 110, 115, 117, 122, 124, 129, 131, 136, 138, 143, 145, 150, 152, 157, 159, 164, 166, 171 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Primitive roots of 7. The first differences are periodic: 2,5,2,5,2,5,.... - Paolo P. Lava, Feb 29 2008

LINKS

Table of n, a(n) for n=1..49.

Index entries for linear recurrences with constant coefficients, signature (1,1,-1).

FORMULA

a(n) = -4 + (1/2)*Sum_{k=0..n} (7 - 3*(-1)^n), with n >= 1. - Paolo P. Lava, Feb 29 2008

a(n) = 7*n - a(n-1) - 6, n > 1. - Vincenzo Librandi, Aug 05 2010

From Bruno Berselli, Sep 08 2010: (Start)

G.f.: x*(3 + 2*x + 2*x^2)/((1+x)*(1-x)^2).

a(n) - a(n-1) - a(n-2) + a(n-3) = 0 for n > 3.

a(n) = (14*n - 5 - 3*(-1)^n)/4. (End)

MAPLE

P:=proc(n, m) local a, i, ok; for i from 1 by 1 to n do if (i^(m-1) mod m)=1 then a:=1; ok:=1; while a<m-1 do if (i^a mod m)=1 then ok:=0; fi; a:=a+1; od; if ok=1 then print(i); fi; fi; od; end: P(100, 7); # Paolo P. Lava, Feb 29 2008

CROSSREFS

Sequence in context: A285415 A275668 A212537 * A263652 A285679 A093661

Adjacent sequences:  A047386 A047387 A047388 * A047390 A047391 A047392

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified February 18 05:48 EST 2018. Contains 299298 sequences. (Running on oeis4.)