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Template:Sequence of the Day for July 31

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Intended for: July 31, 2012

Timetable

  • First draft entered by Alonso del Arte on April 30, 2011
  • Draft reviewed by Daniel Forgues on May 6, 2011
  • Draft approved by Alonso del Arte on July 28, 2011
Yesterday's SOTD * Tomorrow's SOTD

The line below marks the end of the <noinclude> ... </noinclude> section.



A173419: Length of shortest computation yielding
n, n   ≥   1,
using addition, subtraction and multiplication.
{ 0, 1, 2, 2, 3, 3, 4, 3, 3, 4, 4, 4, 5, ... }
So you start with
x0 = 1, xm = n
and then through successive
xk = xi + xj
,
xk = xi xj
, or
xk = xi  −  xj
operations for some
0   ≤   i, j < k
, you get to
n
. The fun is of course getting there in as few steps as possible. Prime
n
are not necessarily more difficult to get to than their neighbors: 29, for example, requires five operations, just as 28 and 30 do.