|
%I #17 Jun 14 2022 02:28:17
%S 2,38,62,346,1298,7898,22682,24382,93022,108194,143362,171982,192718,
%T 264766,587638,986642,1236898,1441042,1604422,2228582,4146434,5070314,
%U 5631718,6687046,10223918,10695182,12465158,14221738,15148522,21718622,23660038,31290398,31390454
%N Numbers k such that sigma(k) = phi(k+1) + phi(k-1).
%H Amiram Eldar, <a href="/A068401/b068401.txt">Table of n, a(n) for n = 1..90</a>
%t Select[Range[2,125*10^5],DivisorSigma[1,#]==Total[EulerPhi[#+{1,-1}]]&] (* _Harvey P. Dale_, Jan 22 2020 *)
%o (PARI) for(n=2,12500000,if(sigma(n)==eulerphi(n+1)+eulerphi(n-1),print1(n,",")))
%Y Cf. A000010, A000203.
%K nonn
%O 1,1
%A _Benoit Cloitre_, Mar 02 2002
%E More terms from _Rick L. Shepherd_, Jul 04 2002
%E More terms from _Amiram Eldar_, Jun 14 2022
|
