The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A005768 Number of convex polygons of length 2n on square lattice whose leftmost bottom vertex is strictly to the left of the rightmost top vertex. (Formerly M1776) 3
 1, 2, 7, 27, 110, 460, 1948, 8296, 35400, 151056, 643892, 2740216, 11639416, 49340080, 208727176, 881212272, 3713043152, 15615663008, 65555425780, 274734294328, 1149506252376, 4802212126704, 20032666552664, 83452195924304, 347192769717040, 1442672957396320 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 REFERENCES M.-P. Delest and G. Viennot, Algebraic languages and polyominoes enumeration, Theoretical Computer Sci., 34 (1984), 169-206. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS FORMULA a(n) = A005436(n) - A005769(n) - A005770(n). G.f.: x^2 * (1 - 8*x + 21*x^2 - 19*x^3 + 4*x^4) / ((1 - 2*x^(1/2))^2 * (1 + 2*x^(1/2))^2*(1 - 2*x)) - 2*x^4*(1 - 4*x)^(-3/2). - Markus Voege (voege(AT)blagny.inria.fr), Nov 28 2003 MATHEMATICA DeleteCases[CoefficientList[Series[x^2*(1 - 8 x + 21 x^2 - 19 x^3 + 4 x^4)/((1 - 2 x^(1/2))^2*(1 + 2 x^(1/2))^2*(1 - 2 x)) - 2 x^4*(1 - 4 x)^(-3/2), {x, 0, 25}], x] , 0] (* Michael De Vlieger, Aug 26 2016 *) CROSSREFS Sequence in context: A026759 A150599 A150600 * A150601 A150602 A150603 Adjacent sequences:  A005765 A005766 A005767 * A005769 A005770 A005771 KEYWORD nonn,easy AUTHOR EXTENSIONS Better description from Markus Voege (voege(AT)blagny.inria.fr), Nov 28 2003 More terms from Sean A. Irvine, Aug 26 2016 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.

Last modified September 22 14:37 EDT 2020. Contains 337291 sequences. (Running on oeis4.)