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A093156
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Another approximation to A000084(n).
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2
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1, 2, 4, 9, 24, 63, 177, 514, 1527, 4625, 14230, 44358, 139779, 444558, 1425151, 4600339, 14939849, 48778197, 160019885, 527200711, 1743607826, 5786756470, 19266336882, 64331275266, 215377539119, 722840378042, 2431459847364
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| 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
| a(n) is the nearest integer to u(n) (with round(0.5)=0), where u(n) has o.g.f.: U(x)=(5-3*x-2*x^2-sqrt(9-30*x-11*x^2+12*x^3+4*x^4))/2 (Riordan & Shannon)
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CROSSREFS
| A more accurate version of A001573. Cf. A000084, A058585.
Sequence in context: A038664 A148077 A148078 * A148079 A148080 A148081
Adjacent sequences: A093153 A093154 A093155 * A093157 A093158 A093159
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KEYWORD
| nonn
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AUTHOR
| Pab Ter (pabrlos(AT)yahoo.com), May 11 2004
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