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A113319 Decimal expansion of Sum_{k>=0} 1/(k^2+1). 20
2, 0, 7, 6, 6, 7, 4, 0, 4, 7, 4, 6, 8, 5, 8, 1, 1, 7, 4, 1, 3, 4, 0, 5, 0, 7, 9, 4, 7, 5, 0, 0, 0, 0, 4, 9, 0, 4, 4, 5, 6, 5, 6, 2, 6, 6, 4, 0, 3, 8, 1, 6, 6, 6, 5, 5, 7, 5, 0, 6, 2, 4, 8, 4, 3, 9, 0, 1, 5, 4, 2, 4, 7, 9, 1, 8, 3, 1, 0, 0, 2, 1, 7, 4, 3, 5, 6, 5, 5, 5, 1, 7, 5, 9, 3, 9, 5, 4, 9, 1, 8, 7, 6, 5, 1 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Known to be transcendental. After n=2 it is the same as A100554(n).

Imaginary part of psi(I) (for the real part, see A248177). - Stanislav Sykora, Oct 03 2014

REFERENCES

Michel Waldschmidt, Elliptic functions and transcendance, Surveys in number theory, 143-188, Dev. Math., 17, Springer, New York, 2008.

LINKS

Ivan Panchenko, Table of n, a(n) for n = 1..1000

Wikipedia, Digamma function

Index entries for transcendental numbers

FORMULA

Equals 1/2 + Pi / tanh(Pi) / 2.

Equals 1+Integral_{x >= 0} sin(x)/(exp(x)-1) dx. - Robert FERREOL, Jan 12 2016.

EXAMPLE

2.076674047468581174134050794750000490445656266403816665575062484390...

MATHEMATICA

RealDigits[N[Im[PolyGamma[0, I]], 105]][[1]]  (* Vaclav Kotesovec, Oct 03 2014 *)

PROG

(PARI) 1/2+Pi/tanh(Pi)/2

(PARI) imag(psi(I)) \\ - Stanislav Sykora, Oct 03 2014

(PARI) sumnumrat(1/(x^2+1), 0) \\ Charles R Greathouse IV, Jan 20 2022

CROSSREFS

Cf. A013661 (Sum_{i>=1} 1/i^2), A232883 (Sum_{i>=0} 1/(2*i^2+1)). - Bruno Berselli, Dec 02 2013

Cf. A248177.

Essentially the same as A100554 and A259171.

Sequence in context: A228819 A104540 A178818 * A298749 A021832 A160509

Adjacent sequences:  A113316 A113317 A113318 * A113320 A113321 A113322

KEYWORD

nonn,cons,changed

AUTHOR

Benoit Cloitre, Jan 07 2006

EXTENSIONS

Offset changed from 0 to 1 by Bruno Berselli, Dec 02 2013

STATUS

approved

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Last modified January 21 23:33 EST 2022. Contains 350481 sequences. (Running on oeis4.)