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Number of steps needed to reach a prime when the following map is repeatedly applied to n: if n is even then 2n + POD(n) + 1, otherwise 2n - POD(n) - 1, where POD(n) is the product of the digits of n; or -1 if no prime is ever reached.
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%I #5 Dec 15 2017 17:36:03

%S 2,1,1,1,2,1,2,4,5,4,2,4,3,5,5,3,5,3,2,1,3,2,3,4,3,4,3,1,3,1,2,1,4,6,

%T 3,3,5,1,2,6,6,5,1,5,2,4,4,2,1,1,8,4,2,2,3,3,3,1,6,2,4,1,1,5,3,2,3,6,

%U 1,2,2,5,2,4,2,5,5,2,5,13,5,1,2,2,2,7,4,1,5,1,2,3,4,4,4,7,3,1,2,2,2,2,2,4

%N Number of steps needed to reach a prime when the following map is repeatedly applied to n: if n is even then 2n + POD(n) + 1, otherwise 2n - POD(n) - 1, where POD(n) is the product of the digits of n; or -1 if no prime is ever reached.

%e a(8) = 4 because 8 -> 25 -> 39 -> 50 -> 101.

%K base,nonn

%O 1,1

%A _Jason Earls_, Sep 08 2002