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 k such that phi((prime(k)-1)/2) = sigma(k). 1
19, 47, 77, 79, 115, 177, 191, 267, 280, 297, 340, 398, 406, 446, 470, 639, 839, 917, 1240, 1655, 1713, 1778, 1836, 2140, 2157, 4715, 5110, 5269, 6585, 7089, 7965, 8517, 8844, 9785, 10281, 12586, 15279, 16100, 16468, 16732, 17724, 18145, 18256, 20728 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..300 (terms below 10^9, terms 1..130 from G. C. Greubel)
MATHEMATICA
Select[Range[2, 3000], EulerPhi[(Prime[#]-1)/2]==DivisorSigma[1, #]&] (* G. C. Greubel, Oct 13 2018 *)
PROG
(PARI) for(n=2, 45000, if(eulerphi((prime(n)-1)/2)==sigma(n), print1(n, ", ")))
CROSSREFS
Sequence in context: A166148 A059657 A048970 * A201314 A289728 A141973
KEYWORD
easy,nonn
AUTHOR
Benoit Cloitre, Mar 10 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 20:05 EDT 2024. Contains 371254 sequences. (Running on oeis4.)