The OEIS is supported by the many generous donors to the OEIS Foundation.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
Reminder: The OEIS is hiring a new managing editor, and the application deadline is January 26.
%I #16 Feb 01 2024 01:33:33
%S 14,24,308,474,690,1242,2970,9690,10340,13110,18270,26400,161880
%N Numbers k such that sigma(k) = phi((prime(k)+prime(k+1))/2).
%C Are there any odd numbers in the sequence?
%C There are no more terms up to 2500000. - _Rick L. Shepherd_, Aug 29 2002
%C No more terms below 3*10^9. - _Amiram Eldar_, Feb 01 2024
%t Select[Range[2,162000],DivisorSigma[1,#]==EulerPhi[ (Prime[ #]+ Prime[ #+1])/2]&] (* _Harvey P. Dale_, Aug 23 2021 *)
%o (PARI) for(n=2,2500000,if(sigma(n)==eulerphi((prime(n)+prime(n+1))/2),print1(n,",")))
%Y Cf. A000010, A000203.
%K nonn,more
%O 1,1
%A _Benoit Cloitre_, Feb 28 2002
%E More terms from _Rick L. Shepherd_, Aug 29 2002