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Search: id:A049293
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| A049293 |
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Number of subgroups of index 3 in fundamental group of a closed surface of characteristic -n. |
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+0
1
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| 0, 0, 4, 34, 220, 1330, 7924, 47194, 281740, 1685410, 10095844, 60522154, 362968060, 2177301490, 13062263764, 78368897914, 470199235180, 2821152757570, 16926788191684, 101560343302474, 609360900699100
(list; graph; listen)
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OFFSET
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-2,3
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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.
A. D. Mednykh, On the number of subgroups in the fundamental group of a closed surface. Commun. in Algebra, 16, No 10 (1988), 2137-2148.
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FORMULA
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a(n) = 6^(n+1)+3^(n+1)-3*2^(n+1)+1.
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CROSSREFS
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Cf. A003319, A027837, A049290-A049295.
Sequence in context: A002101 A129557 A085695 this_sequence A116430 A155628 A036352
Adjacent sequences: A049290 A049291 A049292 this_sequence A049294 A049295 A049296
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KEYWORD
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easy,nice,nonn
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AUTHOR
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V. A. Liskovets (liskov(AT)im.bas-net.by)
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EXTENSIONS
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More terms from Karen Richardson (s1149414(AT)cedarville.edu)
Corrected by T. D. Noe (noe(AT)sspectra.com), Nov 08 2006
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