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 A253952 Numbers that require three steps to collapse to a single digit in base 4 (written in base 10). 3

%I

%S 43,103,139,154,163,169,223,343,403,463,523,547,553,610,643,649,673,

%T 703,823,847,862,1231,1303,1363,1486,1603,2059,2083,2089,2179,2185,

%U 2209,2239,2434,2563,2569,2593,2623,2689,2731

%N Numbers that require three steps to collapse to a single digit in base 4 (written in base 10).

%C One step consists of taking the number in base 4 and inserting some plus signs between the digits with no restrictions and adding the resulting numbers together in base 4. The numbers given here cannot be taken to a single digit in one or two steps. It is known that three steps always suffice to get to a single digit, and that there are infinitely many numbers that require three steps.

%H Steve Butler, <a href="/A253952/b253952.txt">Table of n, a(n) for n = 1..638</a>

%H S. Butler, R. Graham and R. Stong, <a href="http://arxiv.org/abs/1501.04067">Partition and sum is fast</a>, arXiv:1501.04067 [math.HO], 2014.

%e As an example a(1)=43 which in base 4 can be written as 223. There are then three ways to insert plus signs in the first step:

%e 2+23 22+3 2+2+3

%e This gives the numbers (in base 4) as 31, 31, and 13 respectively. In the second step we have one of the following two:

%e 3+1 1+3

%e In both cases this gives the number (in base 4) of 10. Finally in the third step we have the following:

%e 1+0

%e Which gives 1, a single digit, and we cannot get to a single digit in one or two steps. (Note, the single digit that we reduce to is independent of the sequence of steps taken.)

%Y Cf. A253057, A253058, A253953.

%K nonn,base

%O 1,1

%A _Steve Butler_, Jan 20 2015

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Last modified April 8 08:54 EDT 2020. Contains 333313 sequences. (Running on oeis4.)