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 A306324 Decimal expansion of 2*Pi*tanh(sqrt(5/3)*Pi/2)/sqrt(15). 1
 1, 5, 6, 7, 0, 6, 5, 1, 3, 1, 2, 6, 4, 0, 5, 4, 6, 7, 7, 5, 8, 8, 1, 1, 1, 5, 7, 7, 9, 5, 9, 9, 5, 4, 6, 4, 3, 9, 9, 5, 1, 6, 0, 0, 7, 3, 4, 7, 7, 6, 0, 2, 3, 0, 7, 4, 5, 4, 1, 2, 4, 3, 9, 8, 3, 1, 8, 4, 1, 0, 2, 0, 7, 0, 4, 1, 9, 8, 7, 6, 2, 5, 1, 5, 7, 4, 8, 4, 0, 6, 7, 0, 0, 3, 8, 0, 8, 3, 6, 1, 7, 7, 6, 9, 3, 0, 7, 6, 4, 0, 1, 3, 6, 2, 7, 6, 7, 9, 7, 9 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Decimal expansion of the sum of the reciprocals of the centered triangular numbers (A005448). LINKS Eric Weisstein's World of Mathematics, Centered Triangular Number FORMULA Equals Sum_{k>=1} 1/(3*k*(k - 1)/2 + 1). Equals Sum_{k>=1} 1/A005448(k). EXAMPLE 1.56706513126405467758811157795995464399516007... MATHEMATICA RealDigits[2 Pi Tanh[Sqrt[5/3] Pi/2]/Sqrt[15], 10, 120][[1]] PROG (PARI) 2*Pi*tanh(sqrt(5/3)*Pi/2)/sqrt(15) \\ Michel Marcus, Feb 08 2019 CROSSREFS Cf. A005448, A226985, A228048 (decimal expansion of the sum of the reciprocals of the centered square numbers), A303658. Sequence in context: A200110 A189240 A081820 * A214681 A019978 A030178 Adjacent sequences:  A306321 A306322 A306323 * A306325 A306326 A306327 KEYWORD nonn,cons AUTHOR Ilya Gutkovskiy, Feb 07 2019 STATUS approved

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Last modified April 10 06:54 EDT 2021. Contains 342843 sequences. (Running on oeis4.)