A034184 Not necessarily symmetric n X 3 crossword puzzle grids.

1, 15, 111, 649, 3495, 18189, 93231, 474479, 2406621, 12187137, 61668609, 311938233, 1577602849, 7977940187, 40342860995, 204001993697, 1031568839407, 5216271035257, 26376744398811, 133377264694375

Offset

1,2

Links

Andrew Howroyd, Table of n, a(n) for n = 1..200

Louis Marin, Counting Polyominoes in a Rectangle b X h, arXiv:2406.16413 [cs.DM], 2024. See p. 145.

Formula

Appears to obey a 9-term linear recurrence. - Ralf Stephan, May 05 2004

Empirical g.f.: -x*(x^8-x^7-2*x^6-9*x^5+14*x^4-11*x^3-6*x^2+5*x+1) / ((x-1)*(x^2+2*x-1)*(x^6-7*x^5+x^4+6*x^3-11*x^2+7*x-1)). - Colin Barker, Jun 09 2013

Crossrefs

Row 3 of A292357.

Column sums of A059679.

Cf. A001333, A034182, A034184, A034185, A034186, A034187.

Sequence in context: A290753 A290361 A254869 * A092646 A222117 A105051

Adjacent sequences: A034181 A034182 A034183 * A034185 A034186 A034187

Keyword

nonn

Author

Erich Friedman

Status

approved