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A247043
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Decimal expansion of gamma_2, a lattice sum constant, analog of Euler's constant for two-dimensional lattices.
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1
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6, 7, 0, 9, 0, 8, 3, 0, 7, 8, 8, 2, 4, 7, 8, 8, 0, 6, 0, 8, 5, 2, 7, 1, 5, 9, 9, 2, 5, 3, 8, 5, 3, 4, 2, 6, 8, 1, 6, 2, 6, 0, 9, 7, 1, 7, 9, 7, 6, 7, 2, 5, 3, 5, 0, 5, 8, 3, 6, 1, 7, 6, 7, 5, 0, 0, 0, 7, 0, 3, 2, 9, 9, 9, 4, 3, 6, 8, 4, 9, 8, 6, 2, 5, 8, 2, 4, 1, 4, 7, 5, 3, 0, 8, 5, 9, 6, 1, 9, 4, 5, 5, 4
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OFFSET
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0,1
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REFERENCES
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Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, Sections 1.10 Madelung's constant, p. 80.
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LINKS
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FORMULA
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gamma_2 = (1/4)*(delta_2 + 2*log((sqrt(2) + 1)/(sqrt(2) - 1)) - 4*EulerGamma), where delta_2 is A247042.
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EXAMPLE
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-0.670908307882478806085271599253853426816260971797672535...
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MATHEMATICA
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delta2 = 2*Zeta[1/2]*(Zeta[1/2, 1/4] - Zeta[1/2, 3/4]); gamma2 = (1/4)*(delta2 + 2*Log[(Sqrt[2] + 1)/(Sqrt[2] - 1)] - 4*EulerGamma); RealDigits[gamma2, 10, 103] // First
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PROG
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(PARI) (2*zeta(1/2)*(zetahurwitz(1/2, 1/4)-zetahurwitz(1/2, 3/4)) + 2*log((sqrt(2) + 1)/(sqrt(2) - 1)))/4 - Euler \\ Charles R Greathouse IV, Jan 31 2018
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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