login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A026559 a(n) = T(2*n, n-1), where T is given by A026552. 18
1, 3, 12, 45, 180, 721, 2940, 12069, 49935, 207691, 867900, 3640429, 15319395, 64643580, 273431408, 1158988141, 4921651521, 20934115963, 89173404140, 380355072153, 1624282578215, 6943928981859, 29715239620368, 127276313406125, 545605497876400, 2340694589348376, 10048952593607088, 43170264470594302 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = A026552(2*n, n-1)

MATHEMATICA

T[n_, k_]:= T[n, k]= If[k==0 || k==2*n, 1, If[k==1 || k==2*n-1, Floor[(n+2)/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=A026552 *)

a[n_]:= a[n]= Block[{$RecursionLimit = Infinity}, T[2*n, n-1]];

Table[a[n], {n, 40}] (* G. C. Greubel, Dec 17 2021 *)

PROG

(Sage)

@CachedFunction

def T(n, k): # T = A026552

    if (k==0 or k==2*n): return 1

    elif (k==1 or k==2*n-1): return (n+2)//2

    elif (n%2==0): return T(n-1, k) + T(n-1, k-1) + T(n-1, k-2)

    else: return T(n-1, k) + T(n-1, k-2)

[T(2*n, n-1) for n in (1..40)] # G. C. Greubel, Dec 17 2021

CROSSREFS

Cf. A026552, A026553, A026554, A026555, A026556, A026557, A026558, A026560, A026563, A026566, A026567, A027272, A027273, A027274, A027275, A027276.

Sequence in context: A192467 A151162 A094547 * A188949 A184699 A008781

Adjacent sequences:  A026556 A026557 A026558 * A026560 A026561 A026562

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

Terms a(20) onward added by G. C. Greubel, Dec 17 2021

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 26 05:28 EDT 2022. Contains 356986 sequences. (Running on oeis4.)