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A034184 Not necessarily symmetric n X 3 crossword puzzle grids. 7
1, 15, 111, 649, 3495, 18189, 93231, 474479, 2406621, 12187137, 61668609, 311938233, 1577602849, 7977940187, 40342860995, 204001993697, 1031568839407, 5216271035257, 26376744398811, 133377264694375 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

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

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

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Last modified May 24 10:48 EDT 2019. Contains 323529 sequences. (Running on oeis4.)