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%I #8 Apr 14 2020 07:29:20
%S 0,0,1,0,1,4,1,0,1,6,3,4,1,8,1,0,1,10,11,16,1,14,6,16,6,14,19,8,20,16,
%T 8,0,25,18,1,28,26,30,1,16,10,22,35,36,1,6,25,16,8,6,1,40,28,46,36,8,
%U 49,20,4,16,34,8,1,0,1,58,24,52,52,36,8,64,8,26,31
%N Tower of 8's modulo n.
%C a(n) = (8^(8^(8^(8^ ... )))) mod n, provided sufficient 8's are in the tower such that adding more doesn't affect the value of a(n).
%F a(n) = 8^(A000010(n) + a(A000010(n))) mod n.
%F a(n) = (8^^k) mod n, if n < A246496(k), where ^^ is Knuth's double-arrow notation.
%o (PARI) a(n) = {my(b, c=0, d=n, k=1, x=1); while(k==1, z=x; y=1; b=1; while(z>0, while(y<z, d=eulerphi(d); y++); b=8^b-floor((8^b-1)/d)*d; z=z-1; y=1; d=n); if(c==b, k=0); c=b; x++); b%n; }
%Y Cf. A240162, A245970, A245971, A245972, A245973, A245974, A246496, A332054.
%K nonn
%O 1,6
%A _Jinyuan Wang_, Mar 04 2020
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