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Good morning, I computed the following integral using Integrate in version 12.2 and it gives the wrong result. Can you help me understand what I am doing wrong? Here is the integral:

Integrate[(
 n (1 + n) (1 + 2 n) (3 + 
    2 n) (-HypergeometricPFQ[{1, 1, 1 - 2 n, 4 + 2 n}, {2, 3, 3}, 1] +
     t HypergeometricPFQ[{1, 1, 1 - 2 n, 4 + 2 n}, {2, 3, 3}, t]) Log[
   t])/(-1 + t), {t, 0, 1}, {u, 0, 1}, 
 Assumptions -> n \[Element] Integers && n > 0]

the result is

-(1/6) n (1 + n) (1 + 2 n) (3 + 2 n) \[Pi]^2 HypergeometricPFQ[{1, 1, 
   1 - 2 n, 4 + 2 n}, {2, 3, 3}, 1]

For instance, this result is $-\frac{10 \pi ^2}{3} $ for $n=1$. However if I set $n=1$ inside Integrate or use NIntegrate i get $-17.5$, which is the correct result. Why is there such a difference? Here is the code

NIntegrate[((
   n (1 + n) (1 + 2 n) (3 + 
      2 n) (-HypergeometricPFQ[{1, 1, 1 - 2 n, 4 + 2 n}, {2, 3, 3}, 
        1] + t HypergeometricPFQ[{1, 1, 1 - 2 n, 4 + 2 n}, {2, 3, 3}, 
        t]) Log[t])/(-1 + t)) /. n -> 1, {t, 0, 1}, {u, 0, 1}]

and

Integrate[(
  n (1 + n) (1 + 2 n) (3 + 
     2 n) (-HypergeometricPFQ[{1, 1, 1 - 2 n, 4 + 2 n}, {2, 3, 3}, 
       1] + t HypergeometricPFQ[{1, 1, 1 - 2 n, 4 + 2 n}, {2, 3, 3}, 
       t]) Log[t])/(-1 + t) /. n -> 1, {t, 0, 1}, {u, 0, 1}, 
 Assumptions -> n \[Element] Integers && n > 0]

Thank you for your help.

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  • $\begingroup$ A possible bug. In my version (12.0.0 for Mac OS X x86 (64-bit) (April 7, 2019)), the first integral returns unevaluated, and the second two return -17.5 and -35/2. What version are you using? $\endgroup$
    – march
    Commented Sep 23, 2021 at 15:45
  • 1
    $\begingroup$ This returns unevaluated in 12.3.1 on windows 10. May be there was a bug and WRI fixed it? screen shot !Mathematica graphics it is always best to use latest version of software. $\endgroup$
    – Nasser
    Commented Sep 23, 2021 at 15:45
  • $\begingroup$ This also returns -35/2 in MM 12.3.1 for Mac OS (ARM). $\endgroup$ Commented Sep 23, 2021 at 21:02
  • $\begingroup$ Remains unevaluated for me in "12.2.0 for Mac OS X x86 (64-bit) (December 12, 2020)" as well as in V12.3.1. $\endgroup$
    – Michael E2
    Commented Sep 25, 2021 at 13:36

1 Answer 1

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As n is integer you can try

Table[Integrate[(n (1 + n) (1 + 2 n) (3 + 2 n) 
(-HypergeometricPFQ[{1, 1, 1 - 2 n, 4 + 2 n}, {2, 3, 3}, 1] + 
t HypergeometricPFQ[{1, 1, 1 - 2 n, 4 + 2 n}, {2, 3, 3}, t]) 
Log[t])/(-1 + t), {t, 0, 1}], {n, 1, 10}]

for n up to 10 or higher.

The result -10Pi^2/3 for n=1 is just the integral over the term with the first Hypergeometric.

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