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A027070
a(n) = diagonal sum of right-justified array T given by A027052.
2
1, 1, 1, 4, 6, 12, 31, 73, 183, 476, 1248, 3322, 8943, 24271, 66355, 182538, 504824, 1402682, 3913585, 10959499, 30792445, 86775340, 245204312, 694603032, 1972115945, 5610955925, 15994866669, 45677496204, 130661330526, 374339736820, 1074025873959, 3085699969569, 8876601230175
OFFSET
0,4
LINKS
FORMULA
a(n) = Sum_{k=0..n} A027052(n-k, 2*n-3*k). - Sean A. Irvine, Oct 22 2019
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, 2*n-3*k), k=0..n), n=0..35); # G. C. Greubel, Nov 06 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, 2*n-3*k], {k, 0, n}], {n, 0, 35}] (* G. C. Greubel, Nov 06 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, 2*n-3*k) for k in (0..n)) for n in (0..35)] # G. C. Greubel, Nov 06 2019
CROSSREFS
Sequence in context: A102043 A025017 A133427 * A087785 A366772 A081198
KEYWORD
nonn
EXTENSIONS
More terms from Sean A. Irvine, Oct 22 2019
STATUS
approved