login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A093156 Another approximation to A000084(n). 2
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; text; internal format)
OFFSET

1,2

COMMENTS

A more accurate version of A001573.

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=1..27.

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]

CROSSREFS

Cf. A000084, A058585.

Sequence in context: A261367 A148077 A148078 * A148079 A148080 A148081

Adjacent sequences:  A093153 A093154 A093155 * A093157 A093158 A093159

KEYWORD

nonn

AUTHOR

Pab Ter (pabrlos(AT)yahoo.com), May 11 2004

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 31 18:13 EDT 2021. Contains 346376 sequences. (Running on oeis4.)