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a(n) = 3^n mod 100.
4

%I #29 Jul 30 2024 02:49:48

%S 1,3,9,27,81,43,29,87,61,83,49,47,41,23,69,7,21,63,89,67,1,3,9,27,81,

%T 43,29,87,61,83,49,47,41,23,69,7,21,63,89,67,1,3,9,27,81,43,29,87,61,

%U 83,49,47,41,23,69,7,21,63,89,67

%N a(n) = 3^n mod 100.

%C Period is 20.

%H Vincenzo Librandi, <a href="/A001218/b001218.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Fi#final">Index entries for sequences related to final digits of numbers</a>

%t PowerMod[3, Range[0, 60], 100] (* _Vincenzo Librandi_, Aug 15 2016 *)

%o (PARI) a(n)=lift(Mod(3,100)^n) \\ _Charles R Greathouse IV_, Dec 27 2012

%o (Magma) [Modexp(3, n, 100): n in [0..100]]; // _Vincenzo Librandi_, Aug 15 2016

%Y Cf. A001148, A216096, A216097. - _Zak Seidov_, Jul 27 2014

%K nonn,easy

%O 0,2

%A _N. J. A. Sloane_

%E Definition corrected by _Zak Seidov_, Jul 27 2014