A168427 a(n) = 3^n mod 30.

1, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27, 21, 3, 9, 27

Offset

0,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

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

Formula

From Chai Wah Wu, Jan 22 2023: (Start)

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

G.f.: (-20*x^3 - 7*x^2 - 2*x - 1)/((x - 1)*(x^2 + 1)). (End)

Mathematica

PowerMod[3, Range[0, 90], 30] (* Harvey P. Dale, Nov 04 2011 *)

Prog

(Sage) [power_mod(3, n, 30) for n in range(0, 88)] #
(PARI) a(n)=lift(Mod(3, 30)^n) \\ Charles R Greathouse IV, Mar 22 2016
(Python)
def A168427(n): return (21, 3, 9, 27)[n&3] if n else 1 # Chai Wah Wu, Jan 22 2023

Crossrefs

Cf. A001148.

Sequence in context: A321542 A321540 A036123 * A070344 A070357 A131137

Adjacent sequences: A168424 A168425 A168426 * A168428 A168429 A168430

Keyword

nonn,easy

Author

Zerinvary Lajos, Nov 25 2009

Status

approved