A025569 T(2n-1,n), where T is the array defined in A025564.

1, 4, 22, 120, 665, 3732, 21153, 120835, 694590, 4013088, 23284424, 135580865, 791862354, 4637009300, 27215510265, 160053426720, 942939231825, 5564024727096, 32878367902380, 194530139772844, 1152303896900338, 6832908809693304, 40556775927067299, 240938382783554100

Offset

1,2

Links

Table of n, a(n) for n=1..24.

Prog

(PARI) T(n, k) = if( k<0 || k>2*n, 0, if(n==0, 1, polcoeff( (1 + x + x^2)^n, k)+ polcoeff( (1 + x + x^2)^(n-1), k-1)));
a(n) = T(2*n, n+1); \\ Michel Marcus, Sep 08 2019

Crossrefs

Cf. A025564.

Sequence in context: A155596 A244900 A261193 * A098834 A065983 A236576

Adjacent sequences: A025566 A025567 A025568 * A025570 A025571 A025572

Keyword

nonn

Author

Clark Kimberling

Extensions

a(19) corrected and more terms from Sean A. Irvine, Sep 07 2019

Status

approved