A047783 a(n) = floor(Li(n)).

1, 2, 2, 3, 4, 4, 5, 5, 6, 6, 7, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12, 13, 13, 13, 13, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 17, 17, 17, 17, 18, 18, 18, 18, 19, 19, 19, 19, 20, 20, 20, 20, 21, 21, 21, 21, 22, 22, 22, 22, 23, 23

Offset

2,2

References

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 238.

Links

Robert G. Wilson v, Table of n, a(n) for n = 2..1000

M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].

Formula

a(n) = floor(logarithmic integral(n)). - G. C. Greubel, May 17 2019

Mathematica

Array[Floor[LogIntegral[#]] &, 70, 2] (* Robert G. Wilson v, Feb 23 2017 *)

Prog

(PARI) vector(80, n, n++; floor(real(-eint1(-log(n)))) ) \\ G. C. Greubel, May 17 2019
(Magma) [Floor(LogIntegral(n)): n in [2..80]]; // G. C. Greubel, May 17 2019
(Sage) [floor(li(n)) for n in (2..80)] # G. C. Greubel, May 17 2019

Crossrefs

Cf. A047784 (round), A047785 (ceiling).

Sequence in context: A194177 A348386 A023190 * A321667 A194212 A194208

Adjacent sequences: A047780 A047781 A047782 * A047784 A047785 A047786

Keyword

nonn

Author

N. J. A. Sloane

Status

approved