id:A023645 - OEIS Search Results

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a(n) = tau(n)-1 if n is odd or tau(n)-2 if n is even.

+0
4

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; listen)

	OFFSET	`1,6`
	COMMENT	`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`
	REFERENCES	`CRC Handbook of Combinatorial Designs, 1996, p. 649.`
	LINKS	`Gordon Royle, Transitive Graphs`
	FORMULA	`G.f.: Sum_{n>0} x^(3n)/(1-x^n). - Michael Somos, Apr 29 2003.`
	MAPLE	`with(numtheory); f := n->if n mod 2 = 1 then tau(n)-1 else tau(n)-2; fi;`
	PROGRAM	`(PARI) a(n)=if(n<1, 0, numdiv(n)-2+n%2)`
	CROSSREFS	`Cf. A000005, A023637-A023647.` `Sequence in context: A105149 A068307 A158946 this_sequence A054571 A126865 A104640` `Adjacent sequences: A023642 A023643 A023644 this_sequence A023646 A023647 A023648`
	KEYWORD	`nonn`
	AUTHOR	`N. J. A. Sloane (njas(AT)research.att.com).`
	EXTENSIONS	`More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Dec 03 2001`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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