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A274880
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A statistic on orbital systems over n sectors: the number of orbitals with k restarts.
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10
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1, 1, 2, 5, 1, 4, 2, 18, 11, 1, 10, 8, 2, 65, 57, 17, 1, 28, 28, 12, 2, 238, 252, 116, 23, 1, 84, 96, 54, 16, 2, 882, 1050, 615, 195, 29, 1, 264, 330, 220, 88, 20, 2, 3300, 4257, 2915, 1210, 294, 35, 1, 858, 1144, 858, 416, 130, 24, 2, 12441, 17017, 13013, 6461, 2093, 413, 41, 1
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OFFSET
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0,3
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COMMENTS
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The definition of an orbital system is given in A232500 (see also the illustration there). The number of orbitals over n sectors is counted by the swinging factorial A056040.
A 'restart' of an orbital is a raise which starts from the central circle.
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LINKS
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FORMULA
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For even n>0: T(n,k) = 4*(k+1)*binomial(n,n/2-k-1)/n for k=0..n/2-1 (from A118920).
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EXAMPLE
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Triangle read by rows, n>=0. The length of row n is floor((n+1)/2) for n>=1.
[n] [k=0,1,2,...] [row sum]
[ 0] [1] 1
[ 1] [1] 1
[ 2] [2] 2
[ 3] [5, 1] 6
[ 4] [4, 2] 6
[ 5] [18, 11, 1] 30
[ 6] [10, 8, 2] 20
[ 7] [65, 57, 17, 1] 140
[ 8] [28, 28, 12, 2] 70
[ 9] [238, 252, 116, 23, 1] 630
[10] [84, 96, 54, 16, 2] 252
[11] [882, 1050, 615, 195, 29, 1] 2772
T(6, 2) = 2 because there are two orbitals over 6 segments which have 2 ascents:
[-1, 1, 1, -1, 1, -1] and [1, -1, 1, -1, 1, -1].
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PROG
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(Sage) # uses[unit_orbitals from A274709]
from itertools import accumulate
# Brute force counting
def orbital_restart(n):
if n == 0: return [1]
S = [0]*((n+1)//2)
for u in unit_orbitals(n):
A = list(accumulate(u))
L = [1 if A[i] == 0 and A[i+1] == 1 else 0 for i in (0..n-2)]
S[sum(L)] += 1
return S
for n in (0..12): print(orbital_restart(n))
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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