cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

Showing 1-2 of 2 results.

A076907 Meandric numbers for a river crossing two perpendicular roads at n points, beginning in the (-,-) quadrant and ending in any quadrant.

Original entry on oeis.org

2, 2, 6, 10, 32, 62, 210, 436, 1540, 3346, 12192, 27344, 102054, 234388, 891574, 2085940, 8057844, 19134786, 74864648, 179968564, 711708544
Offset: 0

Views

Author

N. J. A. Sloane and Jon Wild, Nov 26 2002

Keywords

Comments

a(n) = number of ways that a directed curve (or arrow) can start in the (-,-) quadrant, cross the x and y axes at exactly n points and end in any quadrant.

Crossrefs

Cf. A005316, A076876, A076906, A076875 (undirected case).
Cf. A077551 (cross x axis first).

Formula

a(2n+1) = 2*A076906(2n+1).

Extensions

a(6) and a(7) corrected Aug 25 2003
a(7) corrected by Robert Price, Jul 29 2012
a(8)-a(20) from Robert Price, Aug 01 2012

A077556 Meandric numbers for an undirected line crossing two perpendicular roads at n points, beginning in the (-,-) quadrant, crossing x axis first and ending in any quadrant.

Original entry on oeis.org

0, 1, 2, 5, 12, 31, 81, 239
Offset: 0

Views

Author

N. J. A. Sloane and Jon Wild, Aug 25 2003

Keywords

Crossrefs

Similar to A077551 but line is undirected.
Showing 1-2 of 2 results.

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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