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!)
A068474 Numbers n such that phi((prime(n)-1)/2)=sigma(n). 1

%I

%S 19,47,77,79,115,177,191,267,280,297,340,398,406,446,470,639,839,917,

%T 1240,1655,1713,1778,1836,2140,2157,4715,5110,5269,6585,7089,7965,

%U 8517,8844,9785,10281,12586,15279,16100,16468,16732,17724,18145,18256,20728

%N Numbers n such that phi((prime(n)-1)/2)=sigma(n).

%H G. C. Greubel, <a href="/A068474/b068474.txt">Table of n, a(n) for n = 1..130</a>

%t Select[Range[2, 3000], EulerPhi[(Prime[#]-1)/2]==DivisorSigma[1, #]&] (* _G. C. Greubel_, Oct 13 2018 *)

%o (PARI) for(n=2,45000, if(eulerphi((prime(n)-1)/2)==sigma(n),print1(n,",")))

%K easy,nonn

%O 1,1

%A _Benoit Cloitre_, Mar 10 2002

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 17 04:46 EST 2022. Contains 350378 sequences. (Running on oeis4.)