A213013 - OEIS

%I #8 Jun 02 2012 06:49:15

%S 0,2,0,2,2,1,0,8,2,2,8,5,8,2,0,2,8,18,12,8,2,16,8,2,18,26,8,11,2,2,0,

%T 2,2,22,8,31,18,5,32,2,8,27,24,17,16,8,32,43,2,2,44,45,26,2,8,56,40,

%U 47,32,33,2,8,0,57,2,5,36,62,22,60,8,1,68,2,56,57,44,8,32,80,2,2,8,2

%N (2^3^4^5^...^n) mod n

%C a(n) = 0 iff n is a power of 2.

%H Max Alekseyev, <a href="/A213013/b213013.txt">Table of n, a(n) for n = 2..1000</a>

%o (PARI) { a(n,m=n,s=2) = local(g); if(s==n, return(n%m)); g=factor(gcd(s,m)); for(i=1,matsize(g)[1], g[i,2]=valuation(m,g[i,1]); m\=g[i,1]^g[i,2]); g=prod(i=1,matsize(g)[1],g[i,1]^g[i,2]); lift( chinese( Mod(0,g), Mod(s,m)^a(n,eulerphi(m),s+1) )) }

%Y A variant of A092188.

%K nonn

%O 2,2

%A _Max Alekseyev_, Jun 02 2012