This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A047783 #18 Sep 08 2022 08:44:57 %S A047783 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, %T A047783 13,13,13,14,14,14,15,15,15,15,16,16,16,16,17,17,17,17,18,18,18,18,19, %U A047783 19,19,19,20,20,20,20,21,21,21,21,22,22,22,22,23,23 %N A047783 a(n) = floor(Li(n)). %D A047783 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. %H A047783 Robert G. Wilson v, <a href="/A047783/b047783.txt">Table of n, a(n) for n = 2..1000</a> %H A047783 M. Abramowitz and I. A. Stegun, eds., <a href="http://www.convertit.com/Go/ConvertIt/Reference/AMS55.ASP">Handbook of Mathematical Functions</a>, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy]. %F A047783 a(n) = floor(logarithmic integral(n)). - _G. C. Greubel_, May 17 2019 %t A047783 Array[Floor[LogIntegral[#]] &, 70, 2] (* _Robert G. Wilson v_, Feb 23 2017 *) %o A047783 (PARI) vector(80, n, n++; floor(real(-eint1(-log(n)))) ) \\ _G. C. Greubel_, May 17 2019 %o A047783 (Magma) [Floor(LogIntegral(n)): n in [2..80]]; // _G. C. Greubel_, May 17 2019 %o A047783 (Sage) [floor(li(n)) for n in (2..80)] # _G. C. Greubel_, May 17 2019 %Y A047783 Cf. A047784 (round), A047785 (ceiling). %K A047783 nonn %O A047783 2,2 %A A047783 _N. J. A. Sloane_