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Nov 1st, 2014
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  1. f = ((1 - x - y + x y + x Log[x] - x y Log[x] + y Log[y] - x y Log[y] + x y Log[x] Log[y]) Log[1 + x y])/((1 - x) x (1 - y) y Log[x] Log[y])
  2.  
  3. fi = Integrate[f, {x, 0, 1}, {y, 0, 1}]
  4.  
  5. NIntegrate[f, {x, 0, 1}, {y, 0, 1}]
  6.  
  7. (* Out[11]= 0.158253 *)
  8.  
  9. {x -> Exp[-u], y -> Exp[-v]}
  10.  
  11. {u, 0, [Infinity]}, {v, 0, [Infinity]}
  12.  
  13. ff = (1/u - 1/(E^u - 1)) (1/v - 1/(E^v - 1)) Log[1 + E^(-u - v)]
  14.  
  15. NIntegrate[ff, {u, 0, [Infinity]}, {v, 0, [Infinity]}]
  16.  
  17. 0.158253
  18.  
  19. (-1)^(k+1)/k (-(1/(-1 + E^u)) + 1/u) (-(1/(-1 + E^v)) + 1/v) E^(-k u -k v)
  20.  
  21. fi = Sum[(-1)^(k + 1)/k g[k]^2, {k, 1, [Infinity]}]
  22.  
  23. g[k_] := Integrate[(-(1/(-1 + E^u)) + 1/u) E^(-k u), {u, 0, [Infinity]}]
  24.  
  25. g[k] = HarmonicNumber[k] - EulerGamma - Log[k]
  26.  
  27. Table[g[k], {k, 1, 5}]
  28.  
  29. (* {1 - EulerGamma, 3/2 - EulerGamma - Log[2],
  30. 11/6 - EulerGamma - Log[3], 25/12 - EulerGamma - Log[4],
  31. 137/60 - EulerGamma - Log[5]} *)
  32.  
  33. NSum[(-1)^(k + 1)/k g[k]^2, {k, 1, [Infinity]}]
  34.  
  35. (* 0.158253 *)
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