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A008724 floor(n^2/12). 11
0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 21, 24, 27, 30, 33, 36, 40, 44, 48, 52, 56, 60, 65, 70, 75, 80, 85, 90, 96, 102, 108, 114, 120, 126, 133, 140, 147, 154, 161, 168, 176, 184, 192, 200, 208, 216, 225, 234, 243, 252, 261, 270, 280, 290, 300, 310, 320, 330, 341, 352 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

With a different offset, Molien series for 3-dimensional group [2,n] = *22n.

REFERENCES

P. T. Ho, The crossing number of K_{4,n} on the real projective plane, Discr. Math., 304 (2005). 23-33.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..10000

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 189

Index entries for Molien series

Eric Weisstein's World of Mathematics, ToroidalCrossingNumber

Index to sequences with linear recurrences with constant coefficients, signature (2,-1,0,0,0,1,-2,1).

FORMULA

a(n) = a(n-6)+n+1 (if 1, 2, 3, ... has offset 0). - Paul Barry, Jul 14 2004

a(n) = sum(floor(j/6), {j,0,n+2}), a(n-2) = (1/2)floor(n/6)*(2n-4-6*floor(n/6)) [From Mitch Harris, Sep 08 2008]

G.f.: x^4/((1-x)^2*(1-x^6)).

MAPLE

x^4/((1-x)^2*(1-x^6));

MATHEMATICA

s=0; lst={}; Do[AppendTo[lst, s+=n]; AppendTo[lst, s+=n]; AppendTo[lst, s+=n]; AppendTo[lst, s+=n]; AppendTo[lst, s+=n]; AppendTo[lst, s+=n], {n, 0, 5!}]; lst [From Vladimir Joseph Stephan Orlovsky, Mar 14 2010]

PROG

(MAGMA) a008724:=func< n | Floor(n^2/12) >; [ a008724(n): n in [0..70] ];

(PARI) a(n)=n^2\12 \\ Charles R Greathouse IV, Jul 02 2013

CROSSREFS

Cf. A001399.

Sequence in context: A120370 A011866 A174709 * A237118 A112402 A056864

Adjacent sequences:  A008721 A008722 A008723 * A008725 A008726 A008727

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

EXTENSIONS

Minor edits by Klaus Brockhaus, Nov 24 2010

STATUS

approved

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Last modified April 19 21:10 EDT 2014. Contains 240777 sequences.