A268046 Decimal expansion of Sum_{k>0} (k+1)/(k*((k+1)^2+1)).

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

Offset

0,1

Comments

Also, decimal expansion of Integral_{x=0..1} (2 - (1+i)*x^(1-i) - (1-i)*x^(1+i))/(4 - 4*x) dx, where i is the imaginary unit.

Links

Table of n, a(n) for n=0..99.

Formula

Equals (1 + i)*(H(1-i) - i*H(1+i))/4, where H(z) is a harmonic number with complex argument.

Equals (Psi(i-1)-Psi(1)-i-1)/2-Pi*(i-1)*coth(Pi)/4), where Psi(x) is the digamma function. - Peter Luschny, Jan 27 2016

Example

.8742700164962955060062206837771568219820392870536409438069097216969635...

Maple

((1+I)*(harmonic(1-I)-I*harmonic(1+I)))/4:
Re(evalf(%, 101)); # Peter Luschny, Jan 27 2016

Mathematica

(1 + I)*(HarmonicNumber[1 - I] - I*HarmonicNumber[1 + I])/4 // Re // RealDigits[#, 10, 100]& // First (* Jean-François Alcover, Jan 26 2016 *)

Prog

(Sage)
# Warning: Floating point calculation. Adjust precision as needed
# and use some guard digits!
from mpmath import mp, chop, psi, pi, coth
mp.dps = 109; mp.pretty = True
chop((psi(0, I-1)-psi(0, 1)-I-1)/2-pi*(I-1)*coth(pi)/4) # Peter Luschny, Jan 27 2016

Crossrefs

Cf. A268086: (1-i)*(H(1-i)+i*H(1+i))/4.

Sequence in context: A326919 A158288 A193716 * A260060 A260800 A196914

Adjacent sequences: A268043 A268044 A268045 * A268047 A268048 A268049

Keyword

nonn,cons

Author

Bruno Berselli, Jan 26 2016

Status

approved