A175134 - OEIS

A175134

Define a(n) as the number of ways to achieve n from the following procedure. Let R={r(k)} and S={s(k)} each be some permutation of (1,2,3,...,j) for some nonnegative integer j (with R and S being empty sets if j=0). Define (b(0),b(1),...,b(j)) as follows. b(0)=1. b(m) = b(m-1)*r(m) + s(m), for 1<= m <= j. Does b(j) = n? If so, add 1 to the count. Calculate the b(j)'s by taking j over all nonnegative integers, and taking R and S over all permutations for a given j. The total count equals a(n).

1, 1, 0, 0, 2, 1, 1, 0, 0, 0, 0, 0, 2

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OFFSET

1,5

LINKS

Table of n, a(n) for n=1..13.

EXAMPLE

For j = 3, R = (3,2,1) and S=(1,2,3), we get b(3)=13. And for j = 3, R = (3,2,1) and S=(1,3,2), we get b(3)=13. So a(13) is at least 2.

CROSSREFS

Sequence in context: A360003 A287146 A025926 * A027355 A127326 A321923

Adjacent sequences: A175131 A175132 A175133 * A175135 A175136 A175137

KEYWORD

more,nonn

AUTHOR

Leroy Quet, Feb 21 2010

STATUS

approved