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A211520 Number of ordered triples (w,x,y) with all terms in {1,...,n} and w + 4y = 2x. 3
0, 0, 0, 1, 2, 3, 5, 7, 10, 12, 16, 19, 24, 27, 33, 37, 44, 48, 56, 61, 70, 75, 85, 91, 102, 108, 120, 127, 140, 147, 161, 169, 184, 192, 208, 217, 234, 243, 261, 271, 290, 300, 320, 331, 352, 363, 385, 397, 420, 432, 456, 469, 494, 507, 533, 547, 574 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

COMMENTS

For a guide to related sequences, see A211422.

For n > 2: partial sums of A178804. - Reinhard Zumkeller, Nov 15 2014

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 0..10000

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

FORMULA

a(n) = a(n-1)+a(n-2)-a(n-3)+a(n-4)-a(n-5)-a(n-6)+a(n-7).

a(n) = (6*n^2-10*n+3+(2*n-7)*(-1)^n-4*(-1)^((2*n-3-(-1)^n)/4))/32. - Luce ETIENNE, Dec 31 2015

a(n) = Sum_{k=1..floor(n/2)} floor((n-k)/2). - Wesley Ivan Hurt, Apr 01 2017

G.f.: x^3 * (1+x+x^3) / ( (1-x)^3*(1+x)^2*(1+x^2) ). - Joerg Arndt, Apr 02 2017

MATHEMATICA

t[n_] := t[n] = Flatten[Table[w - 2 x + 4 y, {w, 1, n}, {x, 1, n}, {y, 1, n}]]

c[n_] := Count[t[n], 0]

t = Table[c[n], {n, 0, 70}]  (* A211520 *)

FindLinearRecurrence[t]

LinearRecurrence[{1, 1, -1, 1, -1, -1, 1}, {0, 0, 0, 1, 2, 3, 5}, 57] (* Ray Chandler, Aug 02 2015 *)

PROG

(Haskell)

a211520 n = a211520_list !! n

a211520_list = 0 : 0 : 0 : scanl1 (+) a178804_list

-- Reinhard Zumkeller, Nov 15 2014

(PARI) { my(x='x+O('x^66)); concat([0, 0, 0], Vec( x^3*(1+x+x^3) / ( (1-x)^3*(1+x)^2*(1+x^2) ) ) ) } \\ Joerg Arndt, Apr 02 2017

CROSSREFS

Cf. A211422.

Cf. A178804.

Sequence in context: A140690 A004684 A036607 * A248578 A062442 A036964

Adjacent sequences:  A211517 A211518 A211519 * A211521 A211522 A211523

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Apr 14 2012

STATUS

approved

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Last modified June 14 10:04 EDT 2021. Contains 345025 sequences. (Running on oeis4.)