A011938 - OEIS

A011938

a(n) = floor( n*(n-1)*(n-2)*(n-3)/28 ).

0, 0, 0, 0, 0, 4, 12, 30, 60, 108, 180, 282, 424, 612, 858, 1170, 1560, 2040, 2622, 3322, 4152, 5130, 6270, 7590, 9108, 10842, 12814, 15042, 17550, 20358, 23490, 26970, 30822, 35074, 39750, 44880, 50490, 56610, 63270, 70500, 78334, 86802, 95940, 105780

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OFFSET

0,6

LINKS

Colin Barker, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (4,-6,4,-1,0,0,1,-4,6,-4,1).

FORMULA

a(n) = 4*a(n-1) - 6*a(n-2) + 4*a(n-3) - a(n-4) + a(n-7) - 4*a(n-8) + 6*a(n-9) - 4*a(n-10) + a(n-11). - Chai Wah Wu, May 25 2016

G.f.: 2*x^5*(2-2*x+3*x^2-2*x^3+2*x^4) / ((1-x)^5*(1+x+x^2+x^3+x^4+x^5+x^6)). - Colin Barker, May 25 2016

MATHEMATICA

Table[Floor[n (n-1)(n-2)(n-3)/28], {n, 0, 50}] (* Vincenzo Librandi, May 27 2016 *)

LinearRecurrence[{4, -6, 4, -1, 0, 0, 1, -4, 6, -4, 1}, {0, 0, 0, 0, 0, 4, 12, 30, 60, 108, 180}, 50] (* Harvey P. Dale, Aug 10 2024 *)

PROG

(PARI) concat(vector(5), Vec(2*x^5*(2-2*x+3*x^2-2*x^3+2*x^4)/((1-x)^5*(1+x+x^2+x^3+x^4+x^5+x^6)) + O(x^50))) \\ Colin Barker, May 25 2016

(Magma) [Floor(n*(n-1)*(n-2)*(n-3)/28): n in [0..50]]; // Vincenzo Librandi, May 27 2016

(SageMath) [6*binomial(n, 4)//7 for n in range(61)] # G. C. Greubel, Oct 27 2024

CROSSREFS

Cf. A011915.

Sequence in context: A067706 A008261 A099407 * A047177 A048077 A350424

Adjacent sequences: A011935 A011936 A011937 * A011939 A011940 A011941

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved