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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

%I

%S 0,10,25,28,29,32,41

%N 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.

%C This sequence is probably finite.

%C The number of times you need to multiply the square of the digits together before reaching 0 or 1 is equals to n.

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

%t 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

%Y Cf. A003001, A031348, A031349.

%K nonn,hard,fini,base

%O 0,2

%A _Michel Lagneau_, May 22 2013

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Last modified January 23 13:52 EST 2020. Contains 331171 sequences. (Running on oeis4.)