A027046 a(n) = Sum_{k=0..n} T(n,k) * T(n,n+k), with T given by A027023.

1, 2, 5, 16, 65, 286, 1305, 6232, 30377, 150178, 750937, 3785904, 19215865, 98086646, 503087741, 2591128000, 13394476993, 69466312210, 361315132065, 1884242109256, 9849626540337, 51599350440694, 270851460356973

Offset

0,2

Links

G. C. Greubel, Table of n, a(n) for n = 0..1000

Maple

T:= proc(n, k) option remember;
      if k<3 or k=2*n then 1
    else add(T(n-1, k-j), j=1..3)
      fi
    end:
seq(add(T(n, k)*T(n, n+k), k=0..n), n=0..30); # G. C. Greubel, Nov 04 2019

Mathematica

T[n_, k_]:= T[n, k]= If[k<3 || k==2*n, 1, Sum[T[n-1, k-j], {j, 3}]]; Table[Sum[T[n, k]*T[n, n+k], {k, 0, n}], {n, 0, 30}] (* G. C. Greubel, Nov 04 2019 *)

Prog

(SageMath)
@CachedFunction
def T(n, k):
    if (k<3 or k==2*n): return 1
    else: return sum(T(n-1, k-j) for j in (1..3))
[sum(T(n, k)*T(n, n+k) for k in (0..n)) for n in (0..30)] # G. C. Greubel, Nov 04 2019

Crossrefs

Sequence in context: A131178 A389232 A003149 * A369775 A268170 A000522

Adjacent sequences: A027043 A027044 A027045 * A027047 A027048 A027049

Keyword

nonn

Author

Clark Kimberling

Status

approved