This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A256607 #20 Dec 14 2016 13:20:47 %S A256607 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 A256607 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 A256607 10,1,10,2,12,2,6,6,4,6,4,2,12,1,18,4,20,2,1,3 %N A256607 Eventual period of 2^(2^k) mod n. %C A256607 In other words, eventual period of 2 under the map x -> x^2 mod n. %C A256607 a(n) is a divisor of A256608(n). %H A256607 Ivan Neretin, <a href="/A256607/b256607.txt">Table of n, a(n) for n = 1..10000</a> %F A256607 a(n) = A007733(A007733(n)). %e A256607 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 A256607 (Haskell) %o A256607 a256607 = a007733 . fromIntegral . a007733 %o A256607 -- _Reinhard Zumkeller_, Apr 13 2015 %Y A256607 Cf. A001146, A007733, A002326. %Y A256607 First differs from A256608 at n=43. %Y A256607 Column 2 of triangle in A279185. %K A256607 nonn %O A256607 1,7 %A A256607 _Ivan Neretin_, Apr 04 2015