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A023645
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a(n) = tau(n)-1 if n is odd or tau(n)-2 if n is even.
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3
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0, 0, 1, 1, 1, 2, 1, 2, 2, 2, 1, 4, 1, 2, 3, 3, 1, 4, 1, 4, 3, 2, 1, 6, 2, 2, 3, 4, 1, 6, 1, 4, 3, 2, 3, 7, 1, 2, 3, 6, 1, 6, 1, 4, 5, 2, 1, 8, 2, 4, 3, 4, 1, 6, 3, 6, 3, 2, 1, 10, 1, 2, 5, 5, 3, 6, 1, 4, 3, 6, 1, 10, 1, 2, 5, 4, 3, 6, 1, 8, 4, 2, 1, 10, 3, 2, 3, 6, 1, 10, 3, 4, 3, 2, 3, 10, 1, 4, 5, 7, 1, 6, 1, 6
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,6
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COMMENTS
| Vertex-transitive graphs of valency 2 with n nodes.
Number of values of k such that n divided by k leaves a remainder 2. - Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Aug 01 2002
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REFERENCES
| CRC Handbook of Combinatorial Designs, 1996, p. 649.
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LINKS
| Gordon Royle, Transitive Graphs
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FORMULA
| G.f.: Sum_{n>0} x^(3n)/(1-x^n). - Michael Somos, Apr 29 2003.
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MAPLE
| with(numtheory); f := n->if n mod 2 = 1 then tau(n)-1 else tau(n)-2; fi;
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PROG
| (PARI) a(n)=if(n<1, 0, numdiv(n)-2+n%2)
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CROSSREFS
| Cf. A000005, A023637-A023647.
Sequence in context: A105149 A068307 A158946 * A167865 A054571 A126865
Adjacent sequences: A023642 A023643 A023644 * A023646 A023647 A023648
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com).
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EXTENSIONS
| More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Dec 03 2001
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