A005509 Number of unrooted triangulations with reflection symmetry of a disk with 2 internal nodes and n+3 nodes on the boundary.

1, 4, 7, 18, 26, 68, 91, 248, 318, 900, 1122, 3278, 4004, 12012, 14443, 44304, 52598, 164424, 193154, 613700, 714476, 2302344, 2659582, 8677072, 9954860, 32836180, 37442160, 124715430, 141430680, 475237500, 536257995, 1816267680, 2040199590, 6959878200

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

References

• C. F. Earl and L. J. March, Architectural applications of graph theory, pp. 327-355 of R. J. Wilson and L. W. Beineke, editors, Applications of Graph Theory. Academic Press, NY, 1979.
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Andrew Howroyd, Table of n, a(n) for n = 0..500
• C. F. Earl and L. J. March, Architectural applications of graph theory, pp. 327-355 of R. J. Wilson and L. W. Beineke, editors, Applications of Graph Theory. Academic Press, NY, 1979. (Annotated scanned copy)
• C. F. Earl & N. J. A. Sloane, Correspondence, 1980-1981

Crossrefs

Row n=2 of the array in A169809.

Extensions

Terms a(6) and beyond from Andrew Howroyd, Feb 22 2021