

A225974


Multiplicative persistence with squares of decimal digits: smallest number such that the number of iterations of "multiply digits squared" needed to reach 0 or 1 equals n.


2




OFFSET

0,2


COMMENTS

This sequence is probably finite.
The number of times you need to multiply the square of the digits together before reaching 0 or 1 is equals to n.


LINKS

Table of n, a(n) for n=0..6.


EXAMPLE

a(4)= 29 > 4*81 = 324 > 9*4*16 = 576 > 25*49*36 = 44100 > 0 has persistence 4.


MATHEMATICA

lst = {}; n = 0; Do[While[True, k = n; c = 0; While[k > 9, k = Times @@ IntegerDigits[k]^2; c++]; If[c == l, Break[]]; n++]; AppendTo[lst, n], {l, 0, 7}]; lst


CROSSREFS

Cf. A003001, A031348, A031349.
Sequence in context: A048195 A133634 A174051 * A274046 A014090 A154057
Adjacent sequences: A225971 A225972 A225973 * A225975 A225976 A225977


KEYWORD

nonn,hard,fini,base


AUTHOR

Michel Lagneau, May 22 2013


STATUS

approved



