A026531 a(n) = T(n,0) + T(n,1) + ... + T(n,n), T given by A026519.

1, 2, 4, 11, 22, 64, 127, 376, 746, 2222, 4414, 13180, 26215, 78373, 156041, 466840, 930194, 2784266, 5550976, 16620976, 33152042, 99291358, 198115526, 593484440, 1184511095, 3548969075, 7084871668, 21230215328, 42390336619

Offset: 0

Author

Clark Kimberling

Keywords

• nonn

Links

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

Crossrefs

Cf. A026519, A026520, A026521, A026522, A026523, A026524, A026525, A026526, A026527, A026528, A026529, A026530, A026531, A026534, A027262, A027263, A027264, A027265, A027266.

Programs

Mathematica

T[n_, k_]:= T[n, k]= If[k<0 || k>2*n, 0, If[k==0 || k==2*n, 1, If[k==1 || k==2*n-1, Floor[(n+1)/2], If[EvenQ[n], T[n-1, k-2] + T[n-1, k], T[n-1, k-1] + T[n - 1, k-2] + T[n-1, k] ]]]]; (* T = A026519 *)
a[n_]:= a[n]= Block[{$RecursionLimit = Infinity}, Sum[T[n, j], {j,0,n}] ];
Table[a[n], {n, 0, 40}] (* G. C. Greubel, Dec 20 2021 *)

Sage

@CachedFunction
def T(n,k): # T = A026519
    if (k<0 or k>2*n): return 0
    elif (k==0 or k==2*n): return 1
    elif (k==1 or k==2*n-1): return (n+1)//2
    elif (n%2==0): return T(n-1, k) + T(n-1, k-2)
    else: return T(n-1, k) + T(n-1, k-1) + T(n-1, k-2)
@CachedFunction
def a(n): return sum( T(n,k) for k in (0..n) )
[a(n) for n in (0..40)] # G. C. Greubel, Dec 20 2021

Formula

a(n) = Sum_{j=0..n} A026519(n, j).