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 A264746 a(n) is the number of domino towers with n bricks up to horizontal flipping. 3
 1, 2, 6, 15, 44, 126, 374, 1106, 3307, 9877, 29599, 88675, 265932, 797453, 2392089, 7175294, 21525097, 64572513, 193715253, 581137787, 1743406694, 5230197111, 15690571861, 47071649170, 141214890563, 423644479136, 1270933270658, 3812799252359, 11438397268254, 34315190174990 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS A domino tower is a stack of bricks, where (1) each row is offset from the preceding row by half of a brick, (2) the bottom row is contiguous, and (3) each brick is supported from below by at least half of a brick. The number of domino towers with n bricks is given by 3^(n-1). LINKS Andrew Howroyd, Table of n, a(n) for n = 1..1000 FORMULA a(n) = (3^(n-1) + A320314(n))/2 EXAMPLE For n=3, the a(3) = 6 domino towers are: +-------+-------+-------+-------+ |       |       |       |       | +-------+-------+-------+-------+     +-------+     |       | +---+---+---+---+ |       |       | +-------+-------+ +-------+-------+ |       |       | +---+---+---+---+     |       |     +-------+             +-------+             |       | +-------+---+---+---+ |       |       | +-------+-------+     +-------+     |       | +---+---+---+ |       | +---+---+---+     |       |     +-------+         +-------+         |       |     +---+---+---+     |       | +---+---+---+ |       | +-------+ CROSSREFS Cf. A000244, A168368, A320314. Sequence in context: A148438 A148439 A151515 * A052870 A293743 A001444 Adjacent sequences:  A264743 A264744 A264745 * A264747 A264748 A264749 KEYWORD nonn AUTHOR Peter Kagey, Oct 10 2018 EXTENSIONS Terms a(20) and beyond from Andrew Howroyd, Mar 12 2021 STATUS approved

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Last modified June 29 17:41 EDT 2022. Contains 354913 sequences. (Running on oeis4.)