I would like to ask if there are any known methods to compute series like this one ?
∞∑k=02k(∞∑n=0(−1)n(n2k+1+(2k+1))3)
And their names so i can look for them if they exist.
I never studied double sums before that's why i am asking, thanks in advance.
Answer
We have
∞∑k=02k∞∑n=0(−1)n(n2k+1+2k+1)3=∞∑k=02k(2k+1)3−∞∑k=0(122k+3∞∑n=1(−1)n−1(n+2k+12k+1)3)
and
∞∑n=1(−1)n−1(n+a)3=18(ζ(3,12+a2)−ζ(3,1+a2)) . (see: Hurwitz zeta function)
It follows
∞∑k=0122k+3∞∑n=1(−1)n−1(n+2k+12k+1)3=∞∑k=0122k+6(ζ(3,12+2k+12k+2)−ζ(3,1+2k+12k+2))
≈0.05957499...
∞∑k=02k(2k+1)3 is divergent because (2k(2k+1)3)k is not a null sequence and
∞∑k=0(122k+3∞∑n=1(−1)n−1(n+2k+12k+1)3) is convergent therefore the initial series is divergent.
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