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Search: id:A058585
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| 1, 1, 2, 4, 9, 23, 63, 177, 514, 1526, 4624, 14230, 44357, 139779, 444557, 1425151, 4600338, 14939849, 48778197, 160019884, 527200711, 1743607825, 5786756469, 19266336882, 64331275266, 215377539119, 722840378041, 2431459847363
(list; graph; listen)
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OFFSET
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0,3
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REFERENCES
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J. Riordan and C. E. Shannon, The number of two-terminal series-parallel networks, J. Math. Phys., 21 (1942), 83-93. Reprinted in Claude Elwood Shannon: Collected Papers, edited by N. J. A. Sloane and A. D. Wyner, IEEE Press, NY, 1993, pp. 560-570.
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FORMULA
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a(n) = floor(u(n)) where u(n) has g.f. (1/2)*(5-3*x-2*x^2-sqrt(9-30*x-11*x^2+12*x^3+4*x^4)).
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CROSSREFS
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Cf. A000084, A001573, A093156.
Sequence in context: A032010 A032028 A127384 this_sequence A001573 A135307 A000083
Adjacent sequences: A058582 A058583 A058584 this_sequence A058586 A058587 A058588
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KEYWORD
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nonn
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), Dec 26 2000
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