Multiply/Add Consecutive Integers
Leroy Quet
qq-quet at mindspring.com
Mon Feb 2 23:54:17 CET 2004
I was wondering today about the sequence where a(n) is the number of ways
to get to n by:
1 (+,*) 2 (+,*) 3 (+,*) ....(+,*) m = n,
where we have the first m positive integers, in order, each separated by
+ or multiply-by.
Order of operation is followed, and there is no parentheses or
concatenation.
For example, since
15 =
1 + 2 +3*4 =
1 + 2 + 3 + 4 + 5 =
1*2*3 + 4 + 5,
we have a(15) = 3 (or at least 3).
I have, figured by hand (so maybe wrong),
a(k) ->
1, 1, 1, 0, 1, 2, 1, 0, 1, 2, 1, 0, 0, 2, 3,...
And this is not in the EIS.
Is there any closed form for this sequence?
(I assume the minimum n for a given m is n= m(m+1)/2 -1 {1*2, rest are
+'s}, and the maximum n is n= m! +1,{1+2, the rest are *'s}.)
thanks,
Leroy Quet
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