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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A063830 a(n+1) is the smallest odd m whose cototient equals a(n). 0

%I

%S 1,3,9,21,45,117,297,585,1521,3105,6993,14553,43653,90885,185925,

%T 397125,847125,1813125,3238725,7556829,17253789,36910365,94571997,

%U 220301277,475043037,47979336637,183450404605,525019294077

%N a(n+1) is the smallest odd m whose cototient equals a(n).

%F a(n) = Min{x, odd : A051953[ a(n-1) ]=a(n)}; a(1)=1; a(2)=3, least odd prime; a(n) = Min[ Select[ Range[ a, b ], Equal[ #-EulerPhi[ # ], a(n-1) ]& ] ].

%e a(5)=45, cototient(45) = 45 - Phi(45) = 45 - 24 = 21 = a(4). This iteration with even numbers might stop, like {1,2,4,6,10} does if the last computed number has no inverse cototient, like 10 which is a non-cototient number.

%Y Cf. A005278, A051953.

%K nonn

%O 1,2

%A _Labos Elemer_, Aug 21 2001

%E More terms from _David Wasserman_, Jul 23 2002

%E a(26)-a(28) from _Donovan Johnson_, Feb 06 2010

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 August 3 10:43 EDT 2021. Contains 346435 sequences. (Running on oeis4.)