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Search: id:A001131
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| A001131 |
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Number of red-black rooted trees with n-1 internal nodes. |
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+0
1
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| 0, 1, 2, 2, 3, 8, 14, 20, 35, 64, 122, 260, 586, 1296, 2708, 5400, 10468, 19888, 37580, 71960, 140612, 279264, 560544, 1133760, 2310316, 4750368, 9876264, 20788880, 44282696, 95241664, 206150208, 447470464, 970862029, 2100029344
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Are a(2) = a(3) = 2 and a(4) = 3 the only primes in this sequence? - Jonathan Vos Post (jvospost2(AT)yahoo.com), Jun 17 2005
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LINKS
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F. Ruskey, Information on Red-Black Trees
Eric Weisstein's World of Mathematics, Link to a section of The World of Mathematics.
Index entries for sequences related to rooted trees
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FORMULA
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a(1) = 1, a(2) = 2, and for n>2: a(n) = Sum[n/4 =< m =< n/2][(2m)C(n-2m) * a(m)} according to John Moon, as cited in Ruskey. - Jonathan Vos Post (jvospost2(AT)yahoo.com), Jun 17 2005
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MAPLE
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spec := [B, {B=Union(Z, Subst(M, B)), M=Union(Prod(Z, Z), Prod(Z, Z, Z, Z))} ]; [seq(combstruct[count](spec, size=2*n), n=0..40)]; # from njas, Dec 21, 2000. Compare A014535, A037026.
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CROSSREFS
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Sequence in context: A046652 A091681 A076541 this_sequence A019177 A132812 A021821
Adjacent sequences: A001128 A001129 A001130 this_sequence A001132 A001133 A001134
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KEYWORD
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nonn
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AUTHOR
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Frank Ruskey (fruskey(AT)cs.uvic.ca)
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