OFFSET
1,1
COMMENTS
From Simon Demers, Oct 20 2017: (Start)
This an exceptionally nice finite sequence based on a surprisingly simple but nontrivial rule: collapse the number expressed in base 3 by inserting plus signs and adding, while minimizing the number of steps (applications).
Butler et al. (2014) proved that any number written in base 2 can be collapsed to a single digit in at most two steps. Any number written in base 3 can be collapsed to a single digit in at most two steps except, surprisingly, for the 11 numbers listed in this sequence. One thing that separates base 3 from larger bases is that there are only 11 base-3 numbers that require three applications!
Let m be the sum of the digits in base-3 expansion. Butler et al. (2014) showed that candidates for this sequence must have m < 82.
(End)
In base 3, the terms are written as 2102222, 11102222, 12022222, 120022222, 202022221, 1200022222, 2002022221, 2020022221, 12000022222, 20200022221, 202000022221. - Andrey Zabolotskiy, Oct 20 2017
LINKS
Steve Butler, R. L. Graham, Richard Stong, Collapsing numbers in bases 2, 3, and beyond, in Gathering for Gardner 10, 2014.
EXAMPLE
In base 3, one of the possible ways to collapse a(1) in three steps is as follows:
2102222 -> 2102 + 222 = 10101 -> 1 + 01 + 01 = 10 -> 1 + 0 = 1.
CROSSREFS
KEYWORD
nonn,fini,full,nice
AUTHOR
N. J. A. Sloane, Jan 13 2015
STATUS
approved