A124217 Expansion of (1-x-x^2)/(1-2x-x^2+x^4).

1, 1, 2, 5, 11, 26, 61, 143, 336, 789, 1853, 4352, 10221, 24005, 56378, 132409, 310975, 730354, 1715305, 4028555, 9461440, 22221081, 52188297, 122569120, 287865097, 676078233, 1587833266, 3729175645, 8758319459, 20569736330

Offset

0,3

Comments

Diagonal sums of generalized Pascal triangle A124216.

Links

Harvey P. Dale, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (2,1,0,-1).

Formula

a(n)=sum{k=0..floor(n/2), sum{j=0..n-k, C(n-k,j)C(j,2(j-k))2^(j-k)}};

Mathematica

CoefficientList[Series[(1-x-x^2)/(1-2x-x^2+x^4), {x, 0, 40}], x] (* or *) LinearRecurrence[{2, 1, 0, -1}, {1, 1, 2, 5}, 40] (* Harvey P. Dale, Jun 14 2016 *)

Crossrefs

Sequence in context: A238437 A191692 A182015 * A095981 A247471 A082397

Adjacent sequences: A124214 A124215 A124216 * A124218 A124219 A124220

Keyword

easy,nonn

Author

Paul Barry, Oct 19 2006

Status

approved