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0, 12, 56, 132, 240, 380, 552, 756, 992, 1260, 1560, 1892, 2256, 2652, 3080, 3540, 4032, 4556, 5112, 5700, 6320, 6972, 7656, 8372, 9120, 9900, 10712, 11556, 12432, 13340, 14280, 15252, 16256, 17292, 18360, 19460, 20592, 21756, 22952, 24180
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| There is a ball-hating monster that lives in a box. You throw 4 numbered balls into the box. He throws 2 balls out. Repeat. Then a(n) gives the number of ordered possibilities the monster has to throw the balls back at each stage (2,1 is different from 1,2).
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FORMULA
| a(n) = (4(n-1)!)/((4(n-1))-2)!)
a(n)=32*n+a(n-1)-20 (with a(0)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 13 2010]
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EXAMPLE
| a(3)=56 because ((4(3-1)!)/((4(3-1))-2)!))=(8!/6!)=(8*7)=56
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MAPLE
| for n from 1 to 100 do printf(`%d, `, (4*n-4)*(4*n-5)) od: (Sellers)
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CROSSREFS
| Sequence in context: A207102 A009653 A133001 * A069552 A035005 A001386
Adjacent sequences: A104185 A104186 A104187 * A104189 A104190 A104191
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KEYWORD
| nonn,easy
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AUTHOR
| Ruppi Rana (ruppi.rana(AT)gmail.com), Mar 12 2005
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EXTENSIONS
| More terms from James A. Sellers (sellersj(AT)math.psu.edu), Apr 10 2005
Simpler defintion from Ralf Stephan, May 20 2007
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