This site is supported by donations to The OEIS Foundation.



Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing.
Other ways to donate

(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A077014 Number of ways that a directed line (or river) that starts in the south can cross an east-west road n times. 3
2, 1, 2, 2, 6, 8, 28, 42, 162, 262, 1076, 1828, 7852, 13820, 61388, 110954, 505878, 933458, 4345660, 8152860, 38608380, 73424650, 352686780, 678390116, 3298016912, 6405031050, 31461151108, 61606881612, 305327366988, 602188541928, 3007925909860, 5969806669034 (list; graph; refs; listen; history; text; internal format)



The difference between this and A005316 is that here the river can also end up in the southwest. In A005316 it was required to end up in the northeast or southeast.

Or, number of ways that an undirected line that starts and ends anywhere can cross an east-west road n times.


Table of n, a(n) for n=0..31.

S. Legendre, Foldings and Meanders, arXiv preprint arXiv:1302.2025 [math.CO], 2013.

S. Legendre, Foldings and Meanders, Australasian Journal of Combinatorics 58(2) (2014), 275-291.


Equals A005316(n) if n odd, or 2*A005316(n) if n even (because then each solution to A005316 can be reflected in a vertical mirror to give another solution).


A005316 = Cases[Import["https://oeis.org/A005316/b005316.txt", "Table"], {_, _}][[All, 2]];

a[n_] := If[OddQ[n], A005316[[n+1]], 2*A005316[[n+1]] ];

a /@ Range[0, 31] (* Jean-Fran├žois Alcover, Sep 07 2019 *)


Sequence in context: A054706 A081727 A000020 * A093655 A023140 A145859

Adjacent sequences:  A077011 A077012 A077013 * A077015 A077016 A077017




N. J. A. Sloane and Jon Wild, Nov 29 2002



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 December 16 04:05 EST 2019. Contains 330013 sequences. (Running on oeis4.)