login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A073256 a(n) = phi(n-th composite number). 3
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 (list; graph; refs; listen; history; text; internal format)
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 *)

CROSSREFS

Cf. A000010, A002808, A035004, A073255.

Sequence in context: A051495 A286542 A278973 * A166362 A050469 A085730

Adjacent sequences:  A073253 A073254 A073255 * A073257 A073258 A073259

KEYWORD

nonn

AUTHOR

Labos Elemer, Jul 22 2002

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 18 01:05 EST 2020. Contains 330995 sequences. (Running on oeis4.)