

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
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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^(n1).


LINKS

Andrew Howroyd, Table of n, a(n) for n = 1..1000


FORMULA

a(n) = (3^(n1) + A320314(n))/2


EXAMPLE

For n=3, the a(3) = 6 domino towers are:
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+++++
  
+++
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++
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++++
 
++++
 
++
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++++
 
++++
 
++


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



