OFFSET
0,2
COMMENTS
This is also the number of ways to misidentify a solar mode of degree l with modes of lower degree. See paper with Lou Lanzerotti (in preparation). - David J. Thomson, Oct 28 2010
LINKS
R. K. Guy, Conway's prime producing machine, Math. Mag. 56 (1983), no. 1, 26-33 (see p. 33).
FORMULA
a(n) = Sum_{k = 1..n} floor((n+1)/k). - N. J. A. Sloane, Oct 28 2008
Since a(n) = A006218(n+1) - 1, asymptotics and bounds may be obtained from that entry.
EXAMPLE
These are the coefficients of x in the Moebius polynomials, which begin: M(1,x) = 1; M(2,x) = 1 + 2x; M(3,x) = 1 + 4x + 2x^2; M(4,x) = 1 + 7x + 8x^2 + 2x^3; M(5,x) = 1 + 9x + 15x^2 + 10x^3 + 2x^4; M(6,x) = 1 + 13x + 30x^2 + 27x^3 + 12x^4 + 2x^5; M(7,x) = 1 + 15x + 43x^2 + 57x^3 + 39x^4 + 14x^5 + 2x^6; M(8,x) = 1 + 19x + 67x^2 + 108x^3 + 98x^4 + 53x^5 + 16x^6 + 2x^7.
MATHEMATICA
a[n_] := Sum[ Floor[(n+1)/k], {k, 1, n+1}] - 1; Table[a[n], {n, 0, 59}] (* Jean-François Alcover, Jun 18 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Benoit Cloitre and Paul D. Hanna, Nov 10 2002
STATUS
approved