A058585 An approximation to A000084(n).

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

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: A127384 A337721 A369328 * A001573 A135307 A000083

Adjacent sequences: A058582 A058583 A058584 * A058586 A058587 A058588

Keyword

nonn

Author

N. J. A. Sloane, Dec 26 2000

Status

approved