A073725 - OEIS

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A073725

EulerPhi of n-th composite number equals a(n)-th composite number; a(1)=a(2)=0.

0, 0, 1, 2, 1, 1, 2, 3, 3, 2, 3, 6, 5, 3, 11, 6, 10, 6, 3, 9, 11, 9, 14, 6, 10, 14, 9, 6, 11, 14, 13, 9, 28, 11, 20, 14, 10, 27, 14, 24, 18, 9, 19, 24, 20, 32, 11, 20, 29, 14, 14, 24, 27, 24, 42, 14, 20, 37, 27, 14, 45, 28, 39, 27, 14, 51, 29, 42, 31, 51, 20, 28, 42, 27, 20, 32, 32 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,4`
	FORMULA	`See program.`
	EXAMPLE	`Phi of 25th composite number = 10th composite number: n=25: A002808[25]=38, Phi[38]=18=A002808(10) so a(25)=10.`
	MATHEMATICA	`c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x]; G[x_] := x-PrimePi[x]-1; a(n)=G[EulerPhi[c[n]]]`
	CROSSREFS	`Cf. A000010, A002808, A062298.` `Sequence in context: A160325 A054989 A051631 * A055223 A174807 A181572` `Adjacent sequences: A073722 A073723 A073724 * A073726 A073727 A073728`
	KEYWORD	`nonn`
	AUTHOR	`Labos E. (labos(AT)ana.sote.hu), Aug 05 2002`

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Last modified February 16 12:15 EST 2012. Contains 205909 sequences.