A306980 - OEIS

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A306980

Decimal expansion of the sum of the reciprocals of the star numbers (A003154).

1, 1, 5, 9, 1, 7, 3, 3, 1, 9, 6, 3, 2, 1, 7, 4, 6, 9, 5, 0, 7, 8, 5, 6, 6, 6, 2, 4, 0, 6, 7, 4, 3, 7, 8, 7, 6, 8, 4, 4, 6, 3, 5, 5, 1, 1, 9, 5, 5, 9, 3, 9, 5, 5, 3, 9, 0, 2, 4, 4, 9, 7, 4, 6, 9, 9, 6, 9, 5, 3, 5, 6, 5, 1, 4, 1, 1, 6, 8, 4, 3, 4, 5, 0, 0, 4, 2

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OFFSET

1,3

LINKS

Table of n, a(n) for n=1..87.

FORMULA

Equals Sum_{n>=1} 1/(6*n*(n-1) + 1) = x * tan(x) with x = Pi/(2*sqrt(3)).

EXAMPLE

1.15917331963217469507856662406743787684463551195593...

MATHEMATICA

s[n_]:=6*n*(n-1) + 1; RealDigits[Sum[1/s[n], {n, 1, Infinity}], 10, 100][[1]]

CROSSREFS

Cf. A003154, A093766 (Pi/(2*sqrt(3))).

Sequence in context: A010490 A021173 A266553 * A063921 A346044 A334402

Adjacent sequences: A306977 A306978 A306979 * A306981 A306982 A306983

KEYWORD

nonn,cons

AUTHOR

Amiram Eldar, Mar 18 2019

STATUS

approved