OFFSET
-1,3
REFERENCES
Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Section 2.19 Vallée's Constant, p. 161.
FORMULA
Sum_{i >= 1, j >= 1, k >= 1} 1 / ((i*j*k + i + k)^2 * (i*j*k + i*j + i + k + 1)^2).
Equals Sum_{i >= 1, j >= 1} (2*PolyGamma(1,i/(i*j + 1) + 1) - ((i*j + 1) * (i*(3*j + 2) + 3))/(i*j + i + 1)^2)/(i*j + 1)^4, where PolyGamma(1,x) is
the derivative of the digamma function psi(x).
EXAMPLE
0.010278164779066596432382953409878325446354715842376389092373240543961916291...
MATHEMATICA
p3 = NSum[(2*PolyGamma[1, i/(i*j + 1) + 1] - ((i*j + 1)*(i*(3*j + 2) + 3))/(i*j + i + 1)^2)/(i*j + 1)^4, {i, 1, 10^4}, {j, 1, 10^4 - i}, NSumTerms -> 10^3]; Join[{0}, RealDigits[p3, 10, 10][[1]]]
PROG
(Magma) nMax:=120; M:=75; SetDefaultRealField(RealField(160)); S:=[]; sum:=0.0; for n in [1..nMax] do for i in [1..n] do for j in [1..n] do if (i eq n) or (j eq n) then kMin:=1; else kMin:=n; end if; for k in [kMin..n] do sum:=sum+1/((i*j*k + i + k)^2 * (i*j*k + i*j + i + k + 1)^2); end for; end for; end for; S[n]:=sum; end for; t:=[]; for n in [1..#S] do t[n]:=S[n]*n^M; end for; for m in [1..M] do for j in [1..#S-m] do t[j]:=(t[j+1]-t[j])/m; if m eq M then ChangePrecision(t[j], 90); end if; end for; end for; // Jon E. Schoenfield, Feb 18 2018
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Jean-François Alcover, May 17 2016
EXTENSIONS
More digits from Jon E. Schoenfield, Feb 18 2018
STATUS
approved