login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A211521 Number of ordered triples (w,x,y) with all terms in {1,...,n} and w + 2x = 4y. 2
0, 0, 1, 2, 4, 5, 9, 11, 16, 18, 25, 28, 36, 39, 49, 53, 64, 68, 81, 86, 100, 105, 121, 127, 144, 150, 169, 176, 196, 203, 225, 233, 256, 264, 289, 298, 324, 333, 361, 371, 400, 410, 441, 452, 484, 495, 529, 541, 576, 588, 625, 638, 676, 689, 729, 743 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

For a guide to related sequences, see A211422.

LINKS

Colin Barker, Table of n, a(n) for n = 1..1000

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) = (2*n^2-5*n+4-(n-2)*(-1)^n+(-1)^((2*n-1+(-1)^n)/4)-(-1)^((6*n-5+(-1)^n)/4))/8. - Luce ETIENNE, Dec 31 2015

G.f.: x^3*(1 + x + x^2 + x^4) / ((1 - x)^3*(1 + x)^2*(1 + x^2)). - Colin Barker, Dec 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}]  (* A211521 *)

FindLinearRecurrence[t]

LinearRecurrence[{1, 1, -1, 1, -1, -1, 1}, {0, 0, 1, 2, 4, 5, 9}, 56] (* Ray Chandler, Aug 02 2015 *)

PROG

(PARI) concat(vector(2), Vec(x^3*(1 + x + x^2 + x^4) / ((1 - x)^3*(1 + x)^2*(1 + x^2)) + O(x^40))) \\ Colin Barker, Dec 02 2017

CROSSREFS

Cf. A211422.

Sequence in context: A065514 A152186 A085765 * A039871 A161375 A241408

Adjacent sequences:  A211518 A211519 A211520 * A211522 A211523 A211524

KEYWORD

nonn,easy

AUTHOR

Clark Kimberling, Apr 14 2012

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified November 21 01:23 EST 2019. Contains 329348 sequences. (Running on oeis4.)