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Search: id:A027844
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| A027844 |
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Number of subgroups of index n of fundamental group of the non-orientable cycle bundle over the Klein bottle. |
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+0
2
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| 1, 7, 7, 27, 11, 55, 15, 91, 34, 97, 23, 231, 27, 147, 77, 299, 35, 334, 39, 437, 105, 271, 47, 847, 86, 345, 142, 699, 59, 865, 63, 1003, 161, 517, 165, 1590, 75, 615, 189, 1701, 83, 1371, 87, 1391, 374, 835, 95, 3023, 162, 1322, 245, 1821, 107, 2062, 253, 2835
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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From a recent general formula of Stanley's for the number of subgroups in G\times Z.
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REFERENCES
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V. A. Liskovets and A. Mednykh, Enumeration of subgroups in the fundamental groups of orientable circle bundles over surfaces, Commun. in Algebra, 28, No. 4 (2000), 1717-1738.
R. P. Stanley, Enumerative Combinatorics, Cambridge, Vol. 2, 1999; see Problem 5.64.
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FORMULA
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Sum k*b(k), k|n, where b(k) is the number of n-list coverings of the Klein bottle (A046524).
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CROSSREFS
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Cf. A001001, A027845, A046524.
Adjacent sequences: A027841 A027842 A027843 this_sequence A027845 A027846 A027847
Sequence in context: A062368 A059772 A114369 this_sequence A111217 A140252 A095343
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KEYWORD
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nonn,easy,nice
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AUTHOR
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njas
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EXTENSIONS
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More terms from V. A. Liskovets (liskov(AT)im.bas-net.by)
Corrected and extended by Vladeta Jovovic (vladeta(AT)Eunet.yu), Feb 03 2003
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