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A058585 An approximation to A000084(n). 2
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; refs; listen; history; text; internal format)
OFFSET

0,3

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.

LINKS

Table of n, a(n) for n=0..27.

FORMULA

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)).

CROSSREFS

Cf. A000084, A001573, A093156.

Sequence in context: A190277 A274882 A127384 * A001573 A135307 A000083

Adjacent sequences:  A058582 A058583 A058584 * A058586 A058587 A058588

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Dec 26 2000

STATUS

approved

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Last modified February 23 21:23 EST 2018. Contains 299588 sequences. (Running on oeis4.)