Bell #s Generalized: e^e^..^(e^x-1)
Leroy Quet
qqquet at mindspring.com
Fri Jul 25 21:57:20 CEST 2003
I wrote:
>....
>
>But if we want, for a fixed m >= 2, {B(m,k)}, where
>
>sum{k=0 to oo} B(m,k) x^k /k! =
>
>exp(exp(...exp(exp(x)-1)..)),
>
>with m 'exp's,
>
>(therefore, B(2,k) is a standard Bell #)
>
>then:
>
>B(1,k) = 1 for all k >= 0 (violating the generating-function, due to
>B(1,0) = 1, and not 0);
>
>B(m,0) = 1;
>
>and:
>
>B(m,j+1) =
>
>
>sum{k=0 to j} binomial(j,k) B(m-1,k) B(m,j-k)
>
>
Those who have replied about my errors are correct.
The recursion-sum should have been:
sum{k=0 to j} binomial(j,k) B(m-1,k+1) B(m,j-k)
{with a 'k+1' replacing a 'k' as an index}
(unless I am again incorrect)
Then, as noted by others, we should have the generating function with -1
added at every level of exponentation.
By the way, the original erroneous recursion-sum gives the sequences
where {B(r,k)} has a EGF of
b_r(x) = exp(integral{0 to x} b_{r-1}(y) dy)
(I think),
where b_1(x) = exp(x).
(b_2(x) is still e^(e^x-1), in any case.)
Now THIS original/erroneous sequence, at least {B(3,k)}, is not yet in
the EIS.
:)
Thanks,
Leroy
Quet
>
>(If I have not erred)
>
>By the way, {B(3,k)} to start:
>
>1, 1, 2, 6, 23, 106,...
>
>Am I even right about any of this?
>(If not, this would explain why {B(3,k)} is not in the EIS.)
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