Problem 57517. Easy Sequences 90: Triple Summation of a Combinatorial Function
Given a positive integer x, we are asked to evaluate the following triple summation:
The symbol
is the combination function, nchoosek in Matlab. Therefore, we can write the function in Matlab as follows:
>> S = @(x) sum(arrayfun(@(y) sum(arrayfun(@(n) sum(arrayfun(@(k) ((-4)^k*nchoosek(n,k)/nchoosek(2*k,k)),0:n)),0:y)),0:x));
Hence, for
, we have:
>> S(5)
>> ans =
-1.3302
Please round-off the output to the nearest 4 decimal places.
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