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A047785 a(n) = ceiling(Li(n)). 3
2, 3, 3, 4, 5, 5, 6, 6, 7, 7, 8, 8, 8, 9, 9, 9, 10, 10, 10, 11, 11, 11, 12, 12, 12, 13, 13, 13, 14, 14, 14, 14, 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, 23, 23, 24 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

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

Harvey P. Dale, 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) = ceiling(logarithmic integral(n)). - G. C. Greubel, May 17 2019

MATHEMATICA

Ceiling[LogIntegral[Range[2, 70]]] (* Harvey P. Dale, Dec 29 2012 *)

PROG

(PARI) vector(80, n, n++; ceil(real(-eint1(-log(n)))) ) \\ G. C. Greubel, May 17 2019

(MAGMA) [Ceiling(LogIntegral(n)): n in [2..80]]; // G. C. Greubel, May 17 2019

(Sage) [ceil(li(n)) for n in (2..80)] # G. C. Greubel, May 17 2019

CROSSREFS

Cf. A047783 (floor), A047784 (round).

Sequence in context: A005185 A119466 A100922 * A027923 A167743 A020888

Adjacent sequences:  A047782 A047783 A047784 * A047786 A047787 A047788

KEYWORD

nonn

AUTHOR

N. J. A. Sloane

STATUS

approved

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Last modified February 26 05:36 EST 2020. Contains 332276 sequences. (Running on oeis4.)