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

1,1

Links

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

Formula

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

Example

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

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 *)

Crossrefs

Cf. A000010, A002808, A035004, A073255.

Sequence in context: A368157 A286542 A278973 * A166362 A050469 A350229

Adjacent sequences: A073253 A073254 A073255 * A073257 A073258 A073259

Keyword

nonn

Author

Labos Elemer, Jul 22 2002

Status

approved