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A027080 a(n) = Sum_{k=0..2n-2} T(n,k) * T(n,k+2), with T given by A027052. 2
2, 15, 100, 757, 5902, 46907, 377520, 3065809, 25078650, 206416795, 1708129244, 14202265321, 118585167502, 993915161547, 8358970631568, 70518298143329, 596590060985546, 5060232622624651, 43022268222676124, 366575545244139845, 3129747701356459022, 26771150349554898415 (list; graph; refs; listen; history; text; internal format)
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<0 or k>2*n then 0

    elif k=0 or k=2 or k=2*n then 1

    elif k=1 then 0

    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 07 2019

MATHEMATICA

T[n_, k_]:= T[n, k]= If[k<0 || k>2*n, 0, If[k==0 || k==2 || k==2*n, 1, If[k==1, 0, 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 07 2019 *)

PROG

(Sage)

@CachedFunction

def T(n, k):

    if (k<0 or k>2*n): return 0

    elif (k==0 or k==2 or k==2*n): return 1

    elif (k==1): return 0

    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 07 2019

CROSSREFS

Sequence in context: A037641 A288952 A258390 * A208347 A293045 A081018

Adjacent sequences:  A027077 A027078 A027079 * A027081 A027082 A027083

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

More terms from Sean A. Irvine, Oct 22 2019

STATUS

approved

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Last modified October 23 03:37 EDT 2020. Contains 337962 sequences. (Running on oeis4.)