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A073811
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Number of common divisors of n and Phi[n].
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1
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1, 1, 1, 2, 1, 2, 1, 3, 2, 2, 1, 3, 1, 2, 1, 4, 1, 4, 1, 3, 2, 2, 1, 4, 2, 2, 3, 3, 1, 2, 1, 5, 1, 2, 1, 6, 1, 2, 2, 4, 1, 4, 1, 3, 2, 2, 1, 5, 2, 4, 1, 3, 1, 6, 2, 4, 2, 2, 1, 3, 1, 2, 3, 6, 1, 2, 1, 3, 1, 2, 1, 8, 1, 2, 2, 3, 1, 4, 1, 5, 4, 2, 1, 6, 1, 2, 1, 4, 1, 4, 1, 3, 2, 2, 1, 6, 1, 4, 2, 6, 1, 2, 1, 4, 2
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,4
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FORMULA
| a(n)=Card[Intersection[D[n], D[A000010(n)]]].
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EXAMPLE
| n=24: Phi[n]=8; Intersection[{1,2,3,4,6,8,12,24},{1,2,4,8}]={1,2,4,8}, so a(24)=4.
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MATHEMATICA
| g1[x_] := Divisors[x] g2[x_] := Divisors[EulerPhi[x]] ncd[x_] := Length[Intersection[g1[x], g2[x]]] Table[ncd[w], {w, 1, 128}]
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CROSSREFS
| Cf. A000010, A073802, A073808, A073809, A073810.
Sequence in context: A193330 A147810 A055181 * A125030 A116479 A122810
Adjacent sequences: A073808 A073809 A073810 * A073812 A073813 A073814
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KEYWORD
| nonn
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Aug 13 2002
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