login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A050399 Least k such that n = A009195(k) (= gcd(phi(k), k)). 8

%I #20 Dec 19 2015 12:59:53

%S 1,4,9,8,25,18,49,16,27,50,121,36,169,98,225,32,289,54,361,100,147,

%T 242,529,72,125,338,81,196,841,450,961,64,1089,578,1225,108,1369,722,

%U 507,200,1681,294,1849,484,675,1058,2209,144,343,250,2601,676,2809

%N Least k such that n = A009195(k) (= gcd(phi(k), k)).

%C Coincides with A072995 for many terms, but differs, e.g., in n = 20, 40, 52, ... in addition to the zeros in A072995. See also the comments in A072994. - _M. F. Hasler_, Feb 23 2014

%C a(n) <= n^2. - _Robert G. Wilson v_, Feb 27 2014

%H Robert G. Wilson v, <a href="/A050399/b050399.txt">Table of n, a(n) for n = 1..10000</a>

%t t = Table[0, {10000}]; k = 1; While[k < 100000001, a = GCD[k, EulerPhi@ k]; If[a < 10001 && t[[a]] == 0, t[[a]] = k; Print[{a, k}]]; k++]; t (* _Robert G. Wilson v_, Feb 27 2014 *)

%o (PARI) A050399=n->for(k=1,9e9,gcd(eulerphi(k),k)==n&&return(k)) \\ _M. F. Hasler_, Feb 23 2014

%K nonn

%O 1,2

%A _Christian G. Bower_, Nov 15 1999

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

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 10:31 EDT 2024. Contains 371240 sequences. (Running on oeis4.)