A074807 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.

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, 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, 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

Offset

1,1

Links

Table of n, a(n) for n=1..104.

Example

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

Crossrefs

Sequence in context: A331310 A241597 A374164 * A165194 A002951 A331287

Adjacent sequences: A074804 A074805 A074806 * A074808 A074809 A074810

Keyword

base,nonn

Author

Jason Earls, Sep 08 2002

Status

approved