A073256 a(n) = phi(n-th composite number).

2, 2, 4, 6, 4, 4, 6, 8, 8, 6, 8, 12, 10, 8, 20, 12, 18, 12, 8, 16, 20, 16, 24, 12, 18, 24, 16, 12, 20, 24, 22, 16, 42, 20, 32, 24, 18, 40, 24, 36, 28, 16, 30, 36, 32, 48, 20, 32, 44, 24, 24, 36, 40, 36, 60, 24, 32, 54, 40, 24, 64, 42, 56, 40, 24, 72, 44, 60, 46, 72, 32, 42, 60

Offset: 1

Author

Labos Elemer, Jul 22 2002

Keywords

• nonn

Examples

			100th composite is 133; phi(133) = 108 = a(100).
		

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1200

Crossrefs

Cf. A000010, A002808, A035004, A073255.

Programs

Mathematica

c[x_] := FixedPoint[x+PrimePi[ # ]+1&, x]; Table[EulerPhi[c[w]], {w, 1, 128}]
With[{nn=100},EulerPhi[#]&/@Complement[Range[2,nn], Prime[Range[ PrimePi[ nn]]]]] (* Harvey P. Dale, Apr 28 2014 *)
EulerPhi[Select[Range[100],CompositeQ]] (* Harvey P. Dale, Jul 05 2024 *)

Formula

a(n) = A000010(A002808(n)).