A027048 a(n) = Sum_{k=0..2n-2} T(n,k) * T(n,k+2), with T given by A027023.

5, 29, 213, 1633, 12821, 102369, 826305, 6724933, 55108961, 454279229, 3764205941, 31334121045, 261903891425, 2197181330193, 18494163039793, 156140262436597, 1321876222268977, 11219183496737037, 95441562533950341, 813656964557564557, 6950294796825730249

Offset

2,1

Links

G. C. Greubel, Table of n, a(n) for n = 2..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, k+2), k=0..2*n-2), n=2..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, k+2], {k, 0, 2*n-2}], {n, 2, 30}] (* G. C. Greubel, Nov 04 2019 *)

Prog

(Sage)
@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, k+2) for k in (0..2*n-2)) for n in (2..30)] # G. C. Greubel, Nov 04 2019

Crossrefs

Sequence in context: A030522 A091124 A121143 * A356408 A192463 A243952

Adjacent sequences: A027045 A027046 A027047 * A027049 A027050 A027051

Keyword

nonn

Author

Clark Kimberling

Extensions

More terms from Sean A. Irvine, Oct 22 2019

Status

approved