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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
0, 10, 25, 28, 29, 32, 41 (list; graph; refs; listen; history; text; internal format)
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

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Last modified January 21 22:54 EST 2021. Contains 340359 sequences. (Running on oeis4.)