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A257822 Decimal expansion of the absolute value of the imaginary part of li(-A257821). 3
3, 8, 7, 4, 5, 0, 1, 0, 4, 9, 3, 1, 2, 8, 7, 3, 6, 2, 2, 3, 7, 0, 9, 6, 9, 7, 1, 3, 5, 0, 6, 3, 3, 9, 0, 1, 2, 3, 8, 4, 0, 5, 8, 0, 4, 0, 5, 4, 5, 0, 4, 8, 4, 6, 3, 7, 7, 3, 4, 0, 2, 1, 4, 5, 6, 4, 6, 0, 3, 2, 4, 7, 8, 2, 1, 6, 8, 6, 5, 4, 3, 7, 2, 6, 5, 3, 3, 8, 6, 7, 8, 2, 3, 8, 9, 5, 3, 1, 1, 4, 8, 4, 6, 1, 2 (list; constant; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

As discussed in A257820, the absolute value of the imaginary part is continuous and its value is a well behaved function of any real argument, excepting z=+1. The above value corresponds to |imag(li(z))| at z=-A257821, the unique point in the real interval (-infinity,+1) where the corresponding real part is zero.

LINKS

Stanislav Sykora, Table of n, a(n) for n = 1..2000

Eric Weisstein's World of Mathematics, Logarithmic Integral

Wikipedia, Logarithmic integral function

EXAMPLE

3.87450104931287362237096971350633901238405804054504846377340...

MATHEMATICA

RealDigits[Im[LogIntegral[-a/.FindRoot[Re[LogIntegral[-a]]==0, {a, 2}, WorkingPrecision->120]]]][[1]] (* Vaclav Kotesovec, May 11 2015 *)

PROG

(PARI) li(z) = {my(c=z+0.0*I); \\ If z is real, convert it to complex

  if(imag(c)<0, return(-Pi*I-eint1(-log(c))),

  return(+Pi*I-eint1(-log(c)))); }

  root=solve(x=-3, -1, real(li(x)));  \\ Better use excess realprecision

  a=imag(li(root))

CROSSREFS

Cf. A257820, A257821.

Sequence in context: A195435 A134903 A177346 * A201293 A225016 A121992

Adjacent sequences:  A257819 A257820 A257821 * A257823 A257824 A257825

KEYWORD

nonn,cons

AUTHOR

Stanislav Sykora, May 11 2015

STATUS

approved

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Last modified May 22 20:08 EDT 2017. Contains 286906 sequences.