A091725 Decimal expansion of second exponential integral at 1, ExpIntegralEi[1].

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

Offset: 1

Author

Eric W. Weisstein, Feb 01 2004

Keywords

• nonn
• cons

Examples

			1.89511781635593675546652...
		

References

• Jerome Spanier and Keith B. Oldham, "Atlas of Functions", Hemisphere Publishing Corp., 1987, chapter 37, table 37:7:1 at page 355.

Links

• Robert Price, Table of n, a(n) for n = 1..10000
• Zbigniew Gołębiewski, Mateusz Klimczak, Protection Number of Recursive Trees, 2019 Proceedings of the Sixteenth Workshop on Analytic Algorithmics and Combinatorics (ANALCO).
• Eric Weisstein's World of Mathematics, Exponential Integral.
• Eric Weisstein's World of Mathematics, Factorial Sums.
• Eric Weisstein's World of Mathematics, Logarithmic Integral.

Crossrefs

Cf. A001563, A001620, A229837.

Programs

Mathematica

RealDigits[ExpIntegralEi[1], 10, 105][[1]] (* Robert G. Wilson v, Oct 08 2004 *)

PARI

real(-eint1(-1)) \\ Charles R Greathouse IV, Apr 23 2013

Formula

Equals li(e), where li(x) is the logarithmic integral, and gamma + Sum_{n>=1} 1/(n*n!) = A001620 + A229837. - Amiram Eldar, Mar 05 2019