A361938 a(0)=1, a(1)=0; a(n) = floor(n/2)*(a(n-1) + a(n-2)).
1, 0, 1, 1, 4, 10, 42, 156, 792, 3792, 22920, 133560, 938880, 6434640, 51614640, 406344960, 3663676800, 32560174080, 326014657920, 3227173488000, 35531881459200, 387590549472000, 4654346740243200, 55461310186867200, 721387883125324800, 9322190319746304000
Offset: 0
Keywords
Examples
a(0) = 1; a(1) = 0; a(2) = floor(2/2)*(a(1) + a(0)) = 1; a(3) = floor(3/2)*(a(2) + a(1)) = 1; a(4) = floor(4/2)*(a(3) + a(2)) = 4; a(5) = floor(5/2)*(a(4) + a(3)) = 10.
Crossrefs
Cf. A055596.
Programs
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Mathematica
a[0] = 1; a[1] = 0; a[n_] := a[n] = Floor[n/2] * (a[n - 1] + a[n - 2]); Array[a, 30, 0] (* Amiram Eldar, Apr 05 2023 *)
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Python
def seqx_it(n): a0 = 1 a1 = 0 sequence_store = [a0,a1] for i in range (2,n): a2 = (i//2) * (a1 + a0) sequence_store.append(a2) a0 = a1 a1 = a2 return sequence_store
Formula
a(0)=1, a(1)=0; a(n) = floor(n/2)*(a(n-1) + a(n-2)).
Comments