Summation – Series Sum of (60n^2-43n+8)/n^4 * binom(4n-2,2n-1) * binom(2n,n)^-4 = 2?(2)

pireference-requestsummation

Recently through Integer Relation Algorithms I was able to find the following Series For $\pi$ :
$$\sum_{n=1}^{\infty}\left(\frac{60n^{2}-43n+8}{n^{4}}\right)\binom{4n-2}{2n-1}\binom{2n}{n}^{-4}=2\zeta(2)$$

I have checked it upto $1000$ digits of precision.

Is this Series known in Literature?, if it is I would appreciate it if someone could provide the source.

Here is the Wolfram Command for those interested :

N[Sum[((60n^2-43n+8)/(n^4))Binomial[4n-2,2n-1]Binomial[2n,n]^{-4},{n,1000}],1000]-2Zeta[2]

EDIT :

It seems the Degree $8$ Variation has been found by Almkvist in 2010 :

$$\sum_{n=1}^{\infty}\left(\frac{60n^{2}-43n+8}{n^{4}}\right)\binom{4n-2}{2n-1}\binom{2n}{n}^{-4}=2\zeta(2)$$
$$\sum_{n=1}^{\infty}\left(\frac{5460n^{4}-8341n^{3}+4864n^{2}-1280n+128}{n^{8}}\right)\ \binom{4n-2}{2n-1}\binom{2n}{n}^{-8}=6\zeta(4)$$

Rewriting such that the Binomial Terms are the same we get this.

Now I thought that a $\zeta(6)$ variation could be found such that we have $n^{12}$ in the denominator, $-12$ the power of Central Binomial Coefficient and a degree $6$ Polynomial in the numerator.

But no luck using Integer Relation Algorithms.

Best Answer

Given the OP's formula A for $\zeta(2)$, there is a very similar one B for $\zeta(4)$,

\begin{align} A &=\sum_{n=1}^{\infty}\binom{4n-2}{2n-1}\binom{2n}{n}^{-4}\frac{(60n^{2}-43n+2^3)}{n^{4}}\\ A &=\frac{\pi^2}3=2\,\zeta(2)\\[8pt] B &=\sum_{n=1}^{\infty}\binom{4n-3}{2n-1}\binom{2n}{n}^{-8}\frac{(5460n^4-8341n^3+2^8(19)n^2-2^8(5)n+2^7)}{n^8}\\ B &=\frac{\pi^4}{30}=3\,\zeta(4) \end{align}

derived by Almkvist by flipping shifting the sole Ramanujan-type formula for $1/\pi^4$ found by Jim Cullen in 2010. (The terminology "shifting" is used by Guillera in "Ramanujan Series with a Shift".)

I wonder if, using the OP's formula for $\pi^2$, it may be possible to shift it to get a Ramanujan-type formula for $1/\pi^2$?


I. Update (an hour later)

Turns out Formula A is indeed a shifted version of one Guillera's formulas for $1/\pi^2$. Given the polynomial in $A$,

$$60(n+k)^2-43(n+k)+8$$

Let $k=1/2$, and it transforms to $\frac12(120n^2+34n+3)$. We do the same to the polynomial in $B$, and we get two Ramanujan-type formulas,

\begin{align} \frac1{\pi^2} &=\frac{1}{2^{5}}\,\sum_{n=0}^\infty b_3(n)\,\frac{120n^2+34n+3}{2^{4n}}\\[4pt] \frac1{\pi^4} &=\frac{1}{2^{11}}\sum_{n=0}^\infty c_2(n)\frac{43680n^4+20632n^3+4340n^2+466n+21}{2^{12n}} \end{align}

where,

$$b_3(n)=\frac{\big(\tfrac12\big)_n^3\,\big(\tfrac14\big)_n\,\big(\tfrac34\big)_n}{n!^5}, \quad c_2(n)=\frac{\big(\tfrac12\big)_n^7\,\big(\tfrac14\big)_n\,\big(\tfrac34\big)_n}{n!^9} \quad $$

with Pochhammer symbol $(x)_n$.

To recap, the formula for $1/\pi^4$ was found by Cullen and Almkvist flipped shifted it to $\pi^4$. For this post, it was the reverse: the OP found $\pi^2$ and, if we shift it, we recover one of Guillera's formulas for $1/\pi^2$. Suggested further reading for two of Guillera's papers can be found in the comments.


II. Addendum (days later)

"Shifting" an identity does not necessarily lead to a shifted value that is the reciprocal of the first. It may be a totally different value. For example, we use the one by Setness Ramesory in the comments and express it with Pochhammer symbols $(x)_n$,

$$F(k)=\small\sum_{n=1}\frac{\big(\tfrac12+k\big)_n\,\big(1+k\big)_n^3}{\big(\tfrac13+k\big)_n^2\,\big(\tfrac23+k\big)_n^2}\, \frac{145(n+k)^2-104(n+k)+18}{(n+k)^3\,(2(n+k)-1)}\, \left(\frac{2}{27}\right)^{2(n+k)}$$

If $k=0$, then naturally we get Ramesory's,

$$F(0) = \frac{\pi^2}{3}\qquad$$

But if $k=\frac12$, then the shifted value is not the reciprocal, but $\pi$ is an exponent lower and with an added rational,

$$\qquad F\big(\tfrac12\big) = \frac{4\pi}{3}-14\left(\frac23\right)^3$$

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