Generating Function For Eulerian Numbers
The first few rows of Eulerian Numbers are
1
1 1
m 1 4 1 n
1 11 11 1
1 26 66 26 1
1 57 302 302 57 1
etc
These number have a great many interesting properties, and they can
be generated by the simple recurrence E[m,n] = nE[m-1,n] + mE[m,n-1].
However, I never noticed before that they also have the nice generating
function
1 / xe^(-yt) - ye^(-xt) \
f(x,y,t) = ----- ln( --------------------- )
xyt \ x - y /
The coefficient of x^(m-1) y^(n-1) (-t)^(m+n-1) / (m+n)! is
the Eulerian number E[m,n], so we have
1 x + y x^2 + 4xy + y^2
f(x,y,t) = - --- t + ------- t^2 - ----------------- t^3 + ...
2 6 24
Is there a simple procedure for deducing the generating function (if
one exists) for any given array of numbers?
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