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!)
A066993 Integer of the form phi(n)*sigma(n)/n. 1
1, 4, 13, 20, 24, 36, 40, 65, 64, 84, 112, 96, 128, 121, 171, 186, 200, 216, 168, 208, 192, 273, 312, 340, 392, 364, 480, 448, 456, 496, 612, 605, 576, 640, 768, 768, 840, 880, 840, 936, 960, 1105, 992, 1200, 1093, 1280, 1464, 1364, 1152, 1539, 1152, 1664, 1482 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
LINKS
FORMULA
a(n) = sigma(A011775(n))*phi(A011775(n))/A011775(n).
MATHEMATICA
Select[Table[EulerPhi[n] DivisorSigma[1, n]/n, {n, 2000}], IntegerQ] (* Harvey P. Dale, Mar 17 2020 *)
PROG
(PARI) { n=0; for (m=1, 10^10, if ((a=eulerphi(m)*sigma(m)/m) % 1.0 == 0 , write("b066993.txt", n++, " ", a); if (n==1000, return)) ) } \\ Harry J. Smith, Apr 16 2010
CROSSREFS
Cf. A011775.
Sequence in context: A292363 A119048 A241264 * A297884 A298289 A298489
KEYWORD
nonn
AUTHOR
Benoit Cloitre, Jan 27 2002
EXTENSIONS
Missing term a(43)=992 and new term a(53)=1482 added by Harry J. Smith, Apr 16 2010
STATUS
approved

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 1 18:30 EST 2024. Contains 370443 sequences. (Running on oeis4.)