A112476 Diagonal sums of Riordan array (1/(1+x),x(1+x)/(1-x)).

1, -1, 2, 0, 3, 3, 8, 12, 25, 43, 82, 148, 275, 503, 928, 1704, 3137, 5767, 10610, 19512, 35891, 66011, 121416, 223316, 410745, 755475, 1389538, 2555756, 4700771, 8646063, 15902592, 29249424, 53798081, 98950095, 181997602, 334745776, 615693475, 1132436851, 2082876104, 3831006428

Offset

0,3

Comments

Diagonal sums of A112475.

Links

Table of n, a(n) for n=0..39.

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

Formula

G.f.: (1-x)/((1+x)(1-x-x^2-x^3)); a(n)=2a(n-2)+2a(n-3)+a(n-4); a(n)=sum{k=0..floor(n/2), sum{j=0..n-2k, C(k-1, j)C(n-k-j-1, n-2k-j)}.

Crossrefs

Sequence in context: A298814 A343980 A021835 * A370724 A321527 A224226

Adjacent sequences: A112473 A112474 A112475 * A112477 A112478 A112479

Keyword

easy,sign

Author

Paul Barry, Sep 07 2005

Status

approved