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A122555
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Number of isomorphism classes of linking pairings on finite Abelian 2-groups of fixed order 2^n.
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1
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1, 4, 6, 14, 20, 43, 59, 108, 158, 265, 373, 600, 838, 1301, 1797, 2693, 3695, 5379, 7291, 10407, 14023, 19651, 26227, 36166, 47888, 65193, 85731, 115308, 150598, 200420
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| A linking pairing on a finite Abelian group G is a nonsingular symmetric bilinear form G x G --> Q/Z.
The combinatorics of this sequence are surprisingly complicated. The corresponding case when p is odd is easier and is now understood. The sequence is a combinatorial refinement of partitions of integers.
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REFERENCES
| F. Deloup, Monoide des enlacements et facteurs orthogonaux, Algebraic and Geometric Topology, 5 (2005) 419-442.
A. Kawauchi and S. Kojima, Algebraic classification of linking pairings on 3-manifolds, Math. Ann. 253 (1980), 29-42.
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LINKS
| F. Deloup, Monoide des enlacements et facteurs orthogonaux.
F. Deloup, Maple program
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EXAMPLE
| a(2) = 4 because there are 4 nonequivalent linking pairings on finite Abelian groups of order 2^2 = 4: there are two nonequivalent cyclic pairings on Z/4, one direct product of two cyclic pairings on Z/2 and one noncyclic pairing on Z/2 x Z/2.
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CROSSREFS
| Sequence in context: A063811 A157616 A029647 * A097271 A126867 A027632
Adjacent sequences: A122552 A122553 A122554 * A122556 A122557 A122558
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KEYWORD
| nonn
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AUTHOR
| Florian Deloup (deloup(AT)math.ups-tlse.fr), Sep 20 2006
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