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A274054
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Number of modified skew Dyck paths of semilength n such that the area between the x-axis and the path is n*(n+1)/2.
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1
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1, 1, 0, 1, 3, 6, 14, 40, 140, 422, 1346, 4487, 15234, 52632, 183913, 651948, 2336751, 8438406, 30712379, 112603500, 415459873, 1541646225, 5750112809, 21548036621, 81096740799, 306404247854, 1161863199131, 4420429256826, 16869986745367, 64567073382731
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OFFSET
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0,5
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COMMENTS
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A modified skew Dyck path is a path in the first quadrant which begins at the origin, ends on the x-axis, consists of steps U=(1,1) (up), D=(1,-1) (down) and A=(-1,1) (anti-down) so that A and D steps do not overlap.
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LINKS
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FORMULA
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EXAMPLE
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a(1) = 1: /\
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/\
\ \
a(3) = 1: / \
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/\ /\
/ \ /\/\/\ / \
a(4) = 3: /\/ \ , / \ , / \/\ .
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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