A006535 Number of one-sided hexagonal polyominoes with n cells.

1, 1, 3, 10, 33, 147, 620, 2821, 12942, 60639, 286190, 1364621, 6545430, 31586358, 153143956, 745700845, 3644379397, 17869651166, 87877879487, 433301253231, 2141584454057, 10607707971062, 52646117638427, 261756764824964, 1303625908234997, 6502430891223011, 32480041218465452, 162454295068924189, 813541940383789255, 4078750395194965720

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• hard
• nice

References

• J. Meeus, personal communication.
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• John Mason, Table of n, a(n) for n = 1..36
• J. Meeus & N. J. A. Sloane, Correspondence, 1974-1975
• Ed Pegg, Jr., Illustrations of polyforms
• Eric Weisstein's World of Mathematics, Polyhex

Crossrefs

Cf. A000228, A030225, A001207.

Formula

a(n) = 2*A000228(n) - A030225(n).

Extensions

a(7)-a(12) from David W. Wilson

a(13) from Achim Flammenkamp, Feb 15 1999

a(14)-a(20) from Joseph Myers, Sep 21 2002

a(21)-a(30) from John Mason, Jul 18 2023