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a(n) = 4^n mod n.
8

%I #12 Jan 03 2016 17:08:40

%S 0,0,1,0,4,4,4,0,1,6,4,4,4,2,4,0,4,10,4,16,1,16,4,16,24,16,1,4,4,16,4,

%T 0,31,16,9,28,4,16,25,16,4,22,4,36,19,16,4,16,18,26,13,48,4,28,34,16,

%U 7,16,4,16,4,16,1,0,49,4,4,52,64,46,4,64,4,16,49

%N a(n) = 4^n mod n.

%H Harry J. Smith, <a href="/A066602/b066602.txt">Table of n, a(n) for n = 1..1000</a>

%e a(7) = 4 as 4^7 = 16384 = 7*2340 + 4.

%p seq(irem(4^n,n),n=1..75); # _Zerinvary Lajos_, Apr 20 2008

%t Table[PowerMod[4, i, i], {i, 50}]

%o (PARI) { for (n=1, 1000, write("b066602.txt", n, " ", 4^n % n) ) } \\ _Harry J. Smith_, Mar 09 2010

%K base,easy,nonn

%O 1,5

%A _Amarnath Murthy_, Dec 22 2001

%E More terms from _Harvey P. Dale_ and _Robert G. Wilson v_, Dec 23 2001