Eulerians as Weighted Binomial Coefficients
There's a nice relation between Eulerian numbers and the generalized
Bernoulli numbers. Let W(m,n) be a weighted average of the nth powers
of the first m natural numbers, using the Eulerians as the weights.
For example
(1)^5 + 26(2)^5 + 66(3)^5 + 26(4)^5 + (5)^5 777
W(6,5) = --------------------------------------------- = -----
120 2
For m>n it turns out that W(m,n) equals B(-m,n), the generalized
Bernoulli number, which can be defined as the coefficients in the
expansion
inf B(-m,n)
( x/(e^x - 1) )^-m = SUM --------- x^n
n=0 n!
Beginning at the "diagonal" where m=n, the values of W and B begin to
differ, although they differ only half the time on the diagonal.
Specifically, the differences B(-m,m) - W(m,m) for m=0,1,2,3... along
the diagonal are
1, -1/2, 1/6, 0, -1/30, 0, 1/42, 0, -1/30, 0, 5/66, 0, -691/2730, ...
which of course are just the ordinary Bernoulli numbers.
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