OFFSET
0,2
COMMENTS
a(n) is the number of all columns in stack polyominoes of perimeter 2n+4. - Emanuele Munarini, Apr 07 2011
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..200
Guo-Niu Han, Enumeration of Standard Puzzles, 2011. [Cached copy]
Guo-Niu Han, Enumeration of Standard Puzzles, arXiv:2006.14070 [math.CO], 2020.
Index entries for linear recurrences with constant coefficients, signature (6,-11,6,-1).
FORMULA
a(n) = (2/5)*(n + 1)*F(2*n+3) + (1/5)*F(2*n+2) - (4/5)*(n + 1)*F(2*n), where F(n) = A000045(n). - Ralf Stephan, May 13 2004
From Emanuele Munarini, Apr 07 2011: (Start)
a(n) = ((4*n + 5)*F(2*n+1) - (2*n + 1)*F(2*n))/5, where F(n) = A000045(n).
a(n) = Sum_{k=0..n} binomial(2*n-k, k)*(k + 1).
G.f.: (1 - 3*x + 3*x^2)/(1 - 3*x + x^2)^2.
a(n) = 6*a(n-1) - 11*a(n-2) + 6*a(n-3) - a(n-4). (End)
MATHEMATICA
Table[((5+4n)Fibonacci[1+2n]-(1+2n)Fibonacci[2n])/5, {n, 0, 20}] [Emanuele Munarini, Apr 07 2011]
PROG
(Maxima) makelist(((5+4*n)*fib(1+2*n)-(1+2*n)*fib(2*n))/5, n, 0, 20); /* Emanuele Munarini, Apr 07 2011 */
(PARI) Vec((1-3*x+3*x^2)/(1-3*x+x^2)^2+O(x^66)) /* Joerg Arndt, Apr 08 2011 */
CROSSREFS
KEYWORD
nonn,changed
AUTHOR
STATUS
approved