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A365327
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Triangle read by rows: T(n,k) is the number of spanning subgraphs of the n-cycle graph with domination number k.
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1
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2, 3, 1, 4, 3, 1, 0, 11, 4, 1, 0, 11, 15, 5, 1, 0, 10, 26, 21, 6, 1, 0, 0, 43, 49, 28, 7, 1, 0, 0, 33, 98, 80, 36, 8, 1, 0, 0, 22, 126, 189, 120, 45, 9, 1, 0, 0, 0, 141, 322, 325, 170, 55, 10, 1, 0, 0, 0, 89, 462, 671, 517, 231, 66, 11, 1, 0, 0, 0, 46, 480, 1162, 1236, 777, 304, 78, 12, 1, 0, 0, 0, 0, 417, 1586, 2483, 2093, 1118, 390, 91, 13, 1
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OFFSET
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1,1
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COMMENTS
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For n >= 3 the n-cycle graph is a simple graph. In the case of n=1 the graph is a loop and for n=2 a double edge.
The number of spanning subgraphs of the n-cycle graph is given by 2^n which is also the sum of the n-th row Sum_{k=1..n} T(n,k).
The average domination number is given by (Sum_{k=1..n} k*T(n,k))/2^n.
The relative average domination number is given by ((Sum_{k=1..n} k*T(n,k))/2^n)/n.
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LINKS
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FORMULA
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T(n,n) = 1 for n > 1.
T(n,n-1) = T(n-1, n-2) + 1 for n > 3.
T(n,n-2) = T(n-1, n-3) + T(n, n-1) for n > 5.
T(n,n-3) = T(n-1, n-4) + T(n, n-2) - 5 for n > 6.
T(n,n-4) = T(n-1, n-5) + T(n-1, n-4) + 11 + Sum_{i=1..n-9} (i+4) for n > 8.
G.f.:
For n > 3; G(n) = x*(G(n-1) + G(n-2) + 2*G(n-3)) + g(n); where
2*(1-x)*x^(n/3) for n mod 3 = 0.
g(n) = { 0 for n mod 3 = 1.
(1-x)*x^((n+1)/3) for n mod 3 = 2.
For n mod 3 = 0:
T(n,k) = 2*T(n-3,k-1) + T(n-2,k-1) + T(n-1,k-1) + 2 for k = n/3.
T(n,k) = 2*T(n-3,k-1) + T(n-2,k-1) + T(n-1,k-1) - 2 for k = n/3 + 1.
T(n,k) = 2*T(n-3,k-1) + T(n-2,k-1) + T(n-1,k-1) for k >= n/3 + 2.
For n mod 3 = 1:
T(n,k) = 2*T(n-3,k-1) + T(n-2,k-1) + T(n-1,k-1) for k >= (n+2)/3.
For n mod 3 = 2:
T(n,k) = 2*T(n-3,k-1) + T(n-2,k-1) + T(n-1,k-1) + 1 for k = (n+1)/3.
T(n,k) = 2*T(n-3,k-1) + T(n-2,k-1) + T(n-1,k-1) - 1 for k = (n+1)/3 + 1.
T(n,k) = 2*T(n-3,k-1) + T(n-2,k-1) + T(n-1,k-1) for k >= (n+1)/3 + 2.
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EXAMPLE
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Example of spanning subgraphs of cycle with 2 vertices:
Domination number: 2 1 1 1
/\ /\
. . . . . . . .
\/ \/
The triangle T(n,k) begins:
n\k 1 2 3 4 5 6 7 8 9 10 11 12 ...
1: 2
2: 3 1
3: 4 3 1
4: 0 11 4 1
5: 0 11 15 5 1
6: 0 10 26 21 6 1
7: 0 0 43 49 28 7 1
8: 0 0 33 98 80 36 8 1
9: 0 0 22 126 189 120 45 9 1
10: 0 0 0 141 322 325 170 55 10 1
11: 0 0 0 89 462 671 517 231 66 11 1
12: 0 0 0 46 480 1162 1236 777 304 78 12 1
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CROSSREFS
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KEYWORD
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AUTHOR
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STATUS
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approved
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