OFFSET
1,1
COMMENTS
The number of binary pattern classes in the (3,n)-rectangular grid with 2 '1's and (n-2) '0's: two patterns are in same class if one of them can be obtained by a reflection or 180-degree rotation of the other, n<10.
Column k=2 of A226290.
Number of lattice points (x,y) in the region bounded by y < 3x, y > x/2 and x <= n. - Wesley Ivan Hurt, Oct 31 2014
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (2,0,-2,1).
FORMULA
a(n) = 2*a(n-1)-2*a(n-3)+a(n-4) for n>4, a(1)=2, a(2)=6, a(3)=13, a(4)=22.
a(n) = 2*a(n-2)-a(n-4)+10 for n>4, a(1)=2, a(2)=6, a(3)=13, a(4)=22.
a(n) = a(n-1)+a(n-2)-a(n-3)+5 for n>3, a(1)=2, a(2)=6, a(3)=13.
a(n) = 3*a(n-1)-3*a(n-2)+a(n-3)+(-1)^n for n>3, a(1)=2, a(2)=6, a(3)=13.
a(n) = 2*a(n-1)-a(n-2)+2+(1-(-1)^n)/2 for n>2, a(1)=2, a(2)=6.
G.f.: x*(2+2*x+x^2)/((1+x)*(1-x)^3). - Bruno Berselli, Jun 03 2013
MAPLE
MATHEMATICA
CoefficientList[Series[(2 + 2 x + x^2) / ((1 + x) (1 - x)^3), {x, 0, 50}], x] (* Vincenzo Librandi, Sep 04 2013 *)
LinearRecurrence[{2, 0, -2, 1}, {2, 6, 13, 22}, 60] (* Harvey P. Dale, Feb 01 2019 *)
PROG
(Magma) [(10*n^2+4*n+(1-(-1)^n))/8: n in [1..50]]; // Vincenzo Librandi, Sep 04 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Yosu Yurramendi, Jun 02 2013
EXTENSIONS
More terms from Vincenzo Librandi, Sep 04 2013
STATUS
approved