A256607 - OEIS

%I #20 Dec 14 2016 13:20:47

%S 1,1,1,1,1,1,2,1,2,1,4,1,2,2,1,1,1,2,6,1,2,4,10,1,4,2,6,2,3,1,4,1,4,1,

%T 2,2,6,6,2,1,4,2,3,4,2,10,11,1,6,4,1,2,12,6,4,2,6,3,28,1,4,4,2,1,2,4,

%U 10,1,10,2,12,2,6,6,4,6,4,2,12,1,18,4,20,2,1,3

%N Eventual period of 2^(2^k) mod n.

%C In other words, eventual period of 2 under the map x -> x^2 mod n.

%C a(n) is a divisor of A256608(n).

%H Ivan Neretin, <a href="/A256607/b256607.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A007733(A007733(n)).

%e For n=9 the map acts as follows: 2 -> 4 -> 7 -> 4 -> 7 and so on. This means the eventual period is 2, hence a(9)=2.

%o (Haskell)

%o a256607 = a007733 . fromIntegral . a007733

%o -- _Reinhard Zumkeller_, Apr 13 2015

%Y Cf. A001146, A007733, A002326.

%Y First differs from A256608 at n=43.

%Y Column 2 of triangle in A279185.

%K nonn

%O 1,7

%A _Ivan Neretin_, Apr 04 2015