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 A069284 Decimal expansion of li(2) = gamma + log(log(2)) + Sum_{k>=1} log(2)^k / ( k*k! ). 3
 1, 0, 4, 5, 1, 6, 3, 7, 8, 0, 1, 1, 7, 4, 9, 2, 7, 8, 4, 8, 4, 4, 5, 8, 8, 8, 8, 9, 1, 9, 4, 6, 1, 3, 1, 3, 6, 5, 2, 2, 6, 1, 5, 5, 7, 8, 1, 5, 1, 2, 0, 1, 5, 7, 5, 8, 3, 2, 9, 0, 9, 1, 4, 4, 0, 7, 5, 0, 1, 3, 2, 0, 5, 2, 1, 0, 3, 5, 9, 5, 3, 0, 1, 7, 2, 7, 1, 7, 4, 0, 5, 6, 2, 6, 3, 8, 3, 3, 5, 6, 3, 0, 6, 0, 2 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS From Mats Granvik, Jun 14 2013: (Start) The logarithmic integral li(x) = exponential integral Ei(log(x)). The generating function for tau A000005, the number of divisors of n is: Sum_{n >= 1} a(n) x^n = Sum_{k > 0} x^k/(1 - x^k). Another way to write the generating function for tau A000005 is Sum_{n>=1} A000005(n) x^n = Sum_{a=1..Infinity} Sum_{b>=1} x^(a*b). If we instead think of the integral with the same form, evaluate at x = exp(1) = 2.7182818284... = A001113 and set the integration limits to zero and sqrt(log(n)), we get for n >= 0: Logarithmic integral li(n) = Integral_{a = 0..sqrt(log(n))} Integral_{b=0..sqrt(log(n))} exp(1)^(a*b) + EulerGamma + log(log(n)). (End) li(2)-1 is the minimum [known to date, for n>1] of |li(n) - PrimePi(n)|. - Jean-François Alcover, Jul 10 2013 The modern logarithmic integral function li(x) = Integral_{t=0..x} (1/log(t)) replaced the Li(x) = Integral_{t=2..x} (1/log(t)) which was sometimes used because it avoids the singularity at x=1. This constant is the offset between the two functions: li(2) = li(x) - Li(x) = Integral_{t=0..2} (1/log(t)). - Stanislav Sykora, May 09 2015 REFERENCES S. R. Finch, Mathematical Constants, Cambridge, 2003, p. 425. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..5000 Eric Weisstein's World of Mathematics, Logarithmic Integral Wikipedia, Logarithmic integral function EXAMPLE 1.0451637801174927848445888891946131365226155781512015758329... MATHEMATICA RealDigits[ LogIntegral[2], 10, 105][[1]] (* Robert G. Wilson v, Oct 08 2004 *) PROG (PARI) -real(eint1(-log(2))) \\ Charles R Greathouse IV, May 26 2013 CROSSREFS Cf. A069285 (continued fraction), A057754, A057794, A060851. Euler's constant gamma: A001620, log(2): A002162, k*k!: A001563. Sequence in context: A131131 A073241 A094642 * A272638 A299630 A068447 Adjacent sequences:  A069281 A069282 A069283 * A069285 A069286 A069287 KEYWORD nonn,cons AUTHOR Frank Ellermann, Mar 13 2002 EXTENSIONS Replaced several occurrences of "Li" with "li" in order to enforce current conventions. - Stanislav Sykora, May 09 2015 STATUS approved

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Last modified October 15 05:56 EDT 2018. Contains 316202 sequences. (Running on oeis4.)