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A000137
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Series-parallel numbers.
(Formerly M1625 N0636)
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2
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1, 2, 6, 18, 58, 186, 614, 2034, 6818, 22970, 77858, 264970, 905294, 3102434, 10661370, 36722642, 126752218, 438294018, 1518032598, 5265341314, 18286911130, 63586988434, 221342104842, 771235606050, 2689688538646, 9388096331642
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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1,2
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REFERENCES
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J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 142.
N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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Sean A. Irvine, Table of n, a(n) for n = 1..1000
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FORMULA
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G.f.: (1+S)/(1-S), where S = g.f. for A000084.
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CROSSREFS
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Cf. A036654, A036655, A058756, A000084.
Sequence in context: A148458 A148459 A081057 * A151282 A193777 A157004
Adjacent sequences: A000134 A000135 A000136 * A000138 A000139 A000140
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane.
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STATUS
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approved
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