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| | Betti number (Site not responding. Last check: 2007-11-02) |
 | | For the most reasonable spaces(such as compact manifolds, finite simplicial complexes or CW complexes), the sequence of Betti numbers is 0 from some points onwards, and consists of natural numbers. |
 | | The Betti numbers do not take into account any torsion in thehomology groups, but they are very useful basic topological invariants. |
 | | The Betti number sequence for a circle is 1, 1, 0, 0, 0,...; for a two- torus is 1, 2,1, 0, 0, 0,..., and for a three- torus is 1, 3, 3, 1, 0, 0, 0,... |
| www.therfcc.org /betti-number-35909.html (343 words) |
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