Voozh

A026751

a(n) = T(2n-1,n-1), T given by A026747.

1, 4, 17, 74, 327, 1461, 6584, 29879, 136391, 625731, 2883357, 13338421, 61920497, 288368511, 1346873365, 6307694990, 29613690966, 139352892908, 657163401162, 3105304341356, 14701236957028, 69722518168060, 331220099616432

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OFFSET

1,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..500

MAPLE

A026747 := proc(n, k) option remember;

if k=0 or k = n then 1;

elif type(n, 'even') and k <= n/2 then

procname(n-1, k-1)+procname(n-2, k-1)+procname(n-1, k) ;

else

procname(n-1, k-1)+procname(n-1, k) ;

end if ;

end proc:

seq(A026747(2*n-1, n-1), n=1..30); # G. C. Greubel, Oct 29 2019

MATHEMATICA

T[n_, k_]:= T[n, k]= If[k==0 || k==n, 1, If[EvenQ[n] && k<=n/2, T[n-1, k -1] + T[n-2, k-1] + T[n-1, k], T[n-1, k-1] + T[n-1, k] ]]; Table[T[2n-1, n-1], {n, 30}] (* G. C. Greubel, Oct 29 2019 *)

PROG

(SageMath)

@CachedFunction

def T(n, k):

if (k==0 or k==n): return 1

elif (mod(n, 2)==0 and k<=n/2): return T(n-1, k-1) + T(n-2, k-1) + T(n-1, k)

else: return T(n-1, k-1) + T(n-1, k)

[T(2*n-1, n-1) for n in (1..30)] # G. C. Greubel, Oct 29 2019

CROSSREFS

Cf. A026747, A026748, A026749, A026750, A026752, A026753, A026754, A026755, A026756, A026757.

Sequence in context: A125586 A086351 A049027 * A227504 A363496 A218984

Adjacent sequences: A026748 A026749 A026750 * A026752 A026753 A026754