A026546 a(n) = T(2n-1,n-2), T given by A026536.

1, 2, 10, 36, 150, 602, 2485, 10256, 42687, 178300, 747912, 3146936, 13278707, 56163758, 238052050, 1010857520, 4299545769, 18314436414, 78115839734, 333583225740, 1426072211137, 6102528959956, 26138050436822, 112046904456640, 480686415837200, 2063641522153406, 8865329237958042, 38108667849379540

Offset

2,2

Links

G. C. Greubel, Table of n, a(n) for n = 2..300

Formula

a(n) = A026536(2*n-1, n-2).

Mathematica

T[n_, k_]:= T[n, k]= If[k==0 || k==2*n, 1, If[k==1 || k==2*n-1, Floor[n/2], If[EvenQ[n], T[n-1, k-2] +T[n-1, k-1] +T[n-1, k], T[n-1, k-2] +T[n-1, k]] ]];
Table[T[2n-1, n-2], {n, 2, 40}] (* G. C. Greubel, Apr 11 2022 *)

Prog

(SageMath)
@CachedFunction
def T(n, k): # A026536
    if k < 0 or n < 0: return 0
    elif k == 0 or k == 2*n: return 1
    elif k == 1 or k == 2*n-1: return n//2
    elif n % 2 == 1: return T(n-1, k-2) + T(n-1, k)
    return T(n-1, k-2) + T(n-1, k-1) + T(n-1, k)
def A026546(n): return T(2*n-1, n-2)
[A026546(n) for n in (2..40)] # G. C. Greubel, Apr 11 2022

Crossrefs

Cf. A026536.

Sequence in context: A001582 A357035 A370713 * A256105 A151020 A151021

Adjacent sequences: A026543 A026544 A026545 * A026547 A026548 A026549

Keyword

nonn

Author

Clark Kimberling

Extensions

Terms a(20) onward added by G. C. Greubel, Apr 11 2022

Status

approved