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A130168
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(b(n)+b(n+1))/3, where b(n) = A000366(n).
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2
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1, 3, 15, 111, 1131, 15123, 256335, 5364471, 135751731, 4084163643, 144039790455, 5884504366431, 275643776229531, 14673941326078563, 880908054392169375, 59226468571935857991, 4432461082611507366531, 367227420727722013775883, 33514867695588319595233095
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,2
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COMMENTS
| As remarked by Gessel, A000366 has a combinatorial interpretation via a certain 2n X n array; this sequence is for a similar array of size (2n-1) X (n-1).
In effect, Dellac gives a combinatorial reason why the elements of A000366 are alternately -1 and +1 modulo 3. Dellac also shows that all the terms of this sequence are odd.
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REFERENCES
| Hippolyte Dellac, Note sur l'\'elimination, m\'ethode de parall\'elogramme, Annales de la Facult\'e des Sciences de Marseille, XI (1901), 141-164.
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CROSSREFS
| Cf. A000366, A130169.
Sequence in context: A201339 A112936 A001063 * A089945 A135083 A058104
Adjacent sequences: A130165 A130166 A130167 * A130169 A130170 A130171
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KEYWORD
| nonn
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AUTHOR
| D. E. Knuth, Aug 02 2007
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