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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
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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; refs; listen; history; internal format)
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OFFSET
| -2,3
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REFERENCES
| 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
| a(n) = 6^(n+1)+3^(n+1)-3*2^(n+1)+1.
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CROSSREFS
| Cf. A003319, A027837, A049290-A049295.
Sequence in context: A196908 A197075 A085695 * A198687 A116430 A201684
Adjacent sequences: A049290 A049291 A049292 * A049294 A049295 A049296
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KEYWORD
| easy,nice,nonn
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AUTHOR
| V. A. Liskovets (liskov(AT)im.bas-net.by)
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EXTENSIONS
| 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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