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A011886 a(n) = floor(n*(n-1)*(n-2)/4). 1
0, 0, 0, 1, 6, 15, 30, 52, 84, 126, 180, 247, 330, 429, 546, 682, 840, 1020, 1224, 1453, 1710, 1995, 2310, 2656, 3036, 3450, 3900, 4387, 4914, 5481, 6090, 6742, 7440, 8184, 8976, 9817, 10710, 11655, 12654, 13708, 14820, 15990, 17220, 18511, 19866, 21285 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (3,-3,1,1,-3,3,-1) [From R. J. Mathar, Apr 15 2010]

FORMULA

a(n) = +3*a(n-1) -3*a(n-2) +a(n-3) +a(n-4) -3*a(n-5) +3*a(n-6) -a(n-7). G.f.: x^3*(1+3*x+2*x^3) / ( (-1+x)^4*(1+x)*(x^2+1) ). - R. J. Mathar, Apr 15 2010

f(n) = floor(Sum_{k=0..n} n*(k+1)/2) for n >= -2. - William A. Tedeschi, Sep 10 2010

MATHEMATICA

Table[Floor[(n(n-1)(n-2))/4], {n, 0, 50}] (* or *) LinearRecurrence[ {3, -3, 1, 1, -3, 3, -1}, {0, 0, 0, 1, 6, 15, 30}, 50] (* Harvey P. Dale, Feb 25 2012 *)

CoefficientList[Series[x^3*(1+3*x+2*x^3)/((-1+x)^4*(1+x)*(x^2+1)), {x, 0, 50}], x] (* Vincenzo Librandi, Jul 07 2012 *)

PROG

(MAGMA) [Floor(n*(n-1)*(n-2)/4): n in [0..50]]; // Vincenzo Librandi, Jul 07 2012

CROSSREFS

Sequence in context: A250121 A024802 A331073 * A212251 A262464 A232169

Adjacent sequences:  A011883 A011884 A011885 * A011887 A011888 A011889

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane.

EXTENSIONS

More terms from William A. Tedeschi, Sep 10 2010

STATUS

approved

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Last modified February 27 04:09 EST 2020. Contains 332299 sequences. (Running on oeis4.)