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Search: id:A116980
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| A116980 |
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Number of ways to arrange integers 1...n so that the sum of each adjacent pair is a triangular number, not counting reversals. |
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+0
1
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| 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 4, 19, 23, 16, 43, 59, 66, 127, 492, 886, 964, 2595, 11426, 36780, 78070, 131232, 423402, 1302893
(list; graph; listen)
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OFFSET
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1,11
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EXAMPLE
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a(9)=1, since {3,7,8,2,4,6,9,1,5} and its reversal are the only permutations
of 1..9 with the given property. Here 3+7, 7+8, 8+2, 4+6, 6+9, 9+1 and 1+5 are all triangular numbers.
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CROSSREFS
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Cf. A051239.
Sequence in context: A043056 A012879 A072178 this_sequence A022135 A028564 A003338
Adjacent sequences: A116977 A116978 A116979 this_sequence A116981 A116982 A116983
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KEYWORD
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nonn
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AUTHOR
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Giovanni Resta (g.resta(AT)iit.cnr.it), Apr 01 2006
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