id:A123246 - OEIS Search Results

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a(n) = PrimePi[n] + (-1)^(PrimePi[n] + 1) (cf. A000720).

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-1, 2, 1, 1, 4, 4, 3, 3, 3, 3, 6, 6, 5, 5, 5, 5, 8, 8, 7, 7, 7, 7, 10, 10, 10, 10, 10, 10, 9, 9, 12, 12, 12, 12, 12, 12, 11, 11, 11, 11, 14, 14, 13, 13, 13, 13, 16, 16, 16, 16, 16, 16, 15, 15, 15, 15, 15, 15, 18, 18, 17, 17, 17, 17, 17, 17, 20, 20, 20, 20, 19, 19, 22, 22, 22, 22, 22, 22, 21, 21, 21, 21, 24, 24, 24, 24, 24, 24, 23, 23, 23, 23 (list; graph; listen)

	OFFSET	`1,2`
	REFERENCES	`Lynn Arthur Steen and J. Arthur Seebach, Jr., Counterexamples in Topology, Dover, New York, 1978, page 134`
	MATHEMATICA	`f[n_] = PrimePi[n] + (-1)^(PrimePi[n] + 1); Table[f[n], {n, 1, 200}]`
	CROSSREFS	`Cf. A055670, A103889.` `Adjacent sequences: A123243 A123244 A123245 this_sequence A123247 A123248 A123249` `Sequence in context: A078121 A119732 A123521 this_sequence A122518 A129704 A057785`
	KEYWORD	`sign`
	AUTHOR	`Roger Bagula (rlbagulatftn(AT)yahoo.com), Oct 07 2006`
	EXTENSIONS	`Edited by njas, Oct 08 2006`

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Last modified October 12 12:19 EDT 2008. Contains 144830 sequences.

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