A093156 -id:A093156 - cp's OEIS frontend

A001573 Another approximation to A000084(n).

1, 2, 4, 9, 23, 63, 177, 514, 1527, 4625, 14230, 44357, 139779, 444558, 1425151, 4600339, 14939849, 48778197, 160019885, 527200711

Offset: 1

N. J. A. Sloane

Appears to have been calculated with very low precision. A093156 is a better version. - Pab Ter (pabrlos(AT)yahoo.com), May 11 2004

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.
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).

J. Riordan and C. E. Shannon, The number of two-terminal series-parallel networks (annotated scanned copy)

Cf. A000084, A058585.

A058585 An approximation to A000084(n).

Original entry on oeis.org

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

N. J. A. Sloane, Dec 26 2000

nonn

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.

Cf. A000084, A001573, A093156.

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)).

cp's OEIS Frontend

A001573 Another approximation to A000084(n).

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