A002460 Nearest integer to exponential integral of n. (Formerly M1378 N0538)

2, 5, 10, 20, 40, 86, 192, 440, 1038, 2492, 6071, 14960, 37198, 93193, 234956, 595561, 1516638, 3877904, 9950907, 25615653, 66127186, 171144671, 443966370, 1154115392, 3005950907, 7842940992, 20496497120, 53645118592, 140599195758

Offset

1,1

References

W. G. Bickley and J. C. P. Miller, Numerical differentiation near the limits of a difference table, Phil. Mag., 33 (1942), 1-12 (plus tables).

A. Fletcher, J. C. P. Miller, L. Rosenhead, and L. J. Comrie, An Index of Mathematical Tables. Vols. 1 and 2, 2nd ed., Blackwell, Oxford and Addison-Wesley, Reading, MA, 1962, Vol. 1, p. 267.

J. W. L. Glaisher, Phil. Trans. Royal Society, 160 (1870), 367-388.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).

N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Formula

Ei(x) = Integral_{-oo..x} (e^t/t) dt.

a(n) ~ exp(n)/n. - Vaclav Kotesovec, May 23 2014

Mathematica

a[n_] := Round[ExpIntegralEi[n]]; Table[a[n], {n, 1, 30}] (* Jean-François Alcover, Dec 19 2011 *)

Prog

(PARI) a(n)=round(-eint1(-n))

Crossrefs

Sequence in context: A084215 A024810 A049938 * A266613 A266462 A293319

Adjacent sequences: A002457 A002458 A002459 * A002461 A002462 A002463

Keyword

nonn,nice

Author

N. J. A. Sloane

Status

approved