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A212415 Number of (w,x,y,z) with all terms in {1,...,n} and w<x>=y<=z. 3
0, 0, 3, 17, 55, 135, 280, 518, 882, 1410, 2145, 3135, 4433, 6097, 8190, 10780, 13940, 17748, 22287, 27645, 33915, 41195, 49588, 59202, 70150, 82550, 96525, 112203, 129717, 149205, 170810, 194680, 220968, 249832, 281435, 315945 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

For a guide to related sequences, see A211795.

Partial sums of A162147. - J. M. Bergot, Jun 21 2013

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1).

FORMULA

a(n) = 5*a(n-1) - 10*a(n-2) + 10*a(n-3) - 5*a(n-4) + a(n-5).

From Bruno Berselli, May 30 2012: (Start)

G.f.: x^2*(3+2*x)/(1-x)^5.

a(n) = (n-1)*n*(n+1)*(5*n+2)/24. (End)

E.g.f.: x^2*(36 + 32*x + 5*x^2)*exp(x)/24. - G. C. Greubel, Jul 11 2019

EXAMPLE

a(3) counts these (w,x,y,z): (1,2,2,2), (1,2,2,3), (1,3,3,3).

MATHEMATICA

t = Compile[{{n, _Integer}}, Module[{s = 0},

(Do[If[w < x >= y <= z, s = s + 1],

{w, 1, #}, {x, 1, #}, {y, 1, #}, {z, 1, #}] &[n]; s)]];

Map[t[#] &, Range[0, 40]]   (* A212415 *)

Table[n*(5*n+2)*(n^2-1)/4!, {n, 0, 40}] (* G. C. Greubel, Jul 11 2019 *)

PROG

(PARI) vector(40, n, n--; n*(5*n+2)*(n^2-1)/4!) \\ G. C. Greubel, Jul 11 2019

(MAGMA) [n*(5*n+2)*(n^2-1)/24: n in [0..40]]; // G. C. Greubel, Jul 11 2019

(Sage) [n*(5*n+2)*(n^2-1)/24 for n in (0..40)] # G. C. Greubel, Jul 11 2019

(GAP) List([0..40], n-> n*(5*n+2)*(n^2-1)/24); # G. C. Greubel, Jul 11 2019

CROSSREFS

Cf. A211795.

Sequence in context: A294134 A258032 A033562 * A152457 A130857 A226719

Adjacent sequences:  A212412 A212413 A212414 * A212416 A212417 A212418

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, May 19 2012

STATUS

approved

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Last modified June 21 18:50 EDT 2021. Contains 345365 sequences. (Running on oeis4.)