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A084248
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Decimal expansion of c = Product_{k>=1} (1 + 1/t(k)) where t(k) = k(k+1)/2 is the k-th triangular number.
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2
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5, 0, 7, 9, 2, 2, 0, 2, 0, 8, 6, 6, 3, 6, 7, 8, 3, 3, 6, 0, 4, 3, 6, 8, 7, 9, 5, 6, 7, 8, 2, 0, 2, 1, 0, 7, 4, 8, 3, 2, 3, 9, 7, 3, 4, 5, 7, 0, 8, 3, 5, 9, 7, 7, 4, 2, 8, 4, 8, 2, 4, 3, 7, 9, 1, 6, 8, 7, 4, 5, 9, 0, 9, 3, 2, 9, 1, 9, 9, 0, 6, 9, 4, 7, 0, 1, 5, 4, 5, 4, 9, 0, 2, 3, 3, 4, 9, 0, 3, 6, 1, 0, 2, 8, 8
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OFFSET
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1,1
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REFERENCES
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Bruce C. Berndt, Ramanujan Notebook part II, Infinite series, Springer Verlag, 1989, p. 241.
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LINKS
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FORMULA
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Equals ((1/2)/Pi)*cosh(Pi/2*sqrt(7)).
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EXAMPLE
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5.07922020866367833604368795...
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MATHEMATICA
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RealDigits[Cosh[Pi/2*Sqrt[7]]/(2*Pi), 10, 120][[1]] (* Amiram Eldar, Jun 01 2023 *)
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PROG
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(PARI) 1/2/Pi*cosh(Pi/2*sqrt(7))
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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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