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A047783
a(n) = floor(Li(n)).
5
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
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
KEYWORD
nonn
STATUS
approved