A084248 - OEIS

A084248

Decimal expansion of c = Product_{k>=1} (1 + 1/t(k)) where t(k) = k(k+1)/2 is the k-th triangular number.

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

1,1

REFERENCES

Bruce C. Berndt, Ramanujan Notebook part II, Infinite series, Springer Verlag, 1989, p. 241.

LINKS

Table of n, a(n) for n=1..105.

FORMULA

Equals ((1/2)/Pi)*cosh(Pi/2*sqrt(7)).

EXAMPLE

5.07922020866367833604368795...

MATHEMATICA