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Search: id:A055581
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| 1, 8, 39, 150, 501, 1524, 4339, 11762, 30705, 77808, 192495, 466926, 1114093, 2621420, 6094827, 14024682, 31981545, 72351720, 162529255, 362807270, 805306341, 1778384868, 3909091299, 8556380130, 18656264161, 40533753824
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OFFSET
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0,2
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COMMENT
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a(n) = number of directed column-convex polyominoes of area n+5 having along the lower contour exactly two reentrant corners. - Emeric Deutsch (deutsch(AT)duke.poly.edu), May 21 2003
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FORMULA
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G.f.: 1/(((1-2*x)^3)*(1-x)^2).
a(n)= A055252(n+4, 4). a(n)= sum(a(j), j=0..n-1)+A045889(n), n >= 1.
a(n)=(n^2-n+4)2^(n+1)-7-n - Emeric Deutsch (deutsch(AT)duke.poly.edu), May 21 2003
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CROSSREFS
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Cf. A055252, A055249, A045889, partial sums of A055580.
Sequence in context: A163687 A060446 A063002 this_sequence A134415 A097787 A144414
Adjacent sequences: A055578 A055579 A055580 this_sequence A055582 A055583 A055584
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KEYWORD
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easy,nonn
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AUTHOR
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Wolfdieter Lang (wolfdieter.lang(AT)physik.uni-karlsruhe.de), May 26 2000
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