login
Numbers k such that A083266(k) is prime.
2

%I #13 Apr 09 2021 09:50:53

%S 2,6,10,15,21,26,28,30,35,38,39,40,42,44,45,46,51,55,60,63,68,69,70,

%T 78,84,93,95,96,102,105,106,116,123,124,126,130,135,136,138,143,146,

%U 150,153,155,166,174,176,178,201,203,205,218,219,221,222,231,232,234,236,240,244,245,246,248,249

%N Numbers k such that A083266(k) is prime.

%C Includes 2*p for p in A157468.

%H Robert Israel, <a href="/A343148/b343148.txt">Table of n, a(n) for n = 1..10000</a>

%e a(3) = 10 is a term because A083266(10) = 37 is prime.

%p f:= n -> numtheory:-sigma(n) + n*numtheory:-phi(n)/2 - 1:

%p select(t -> isprime(f(t)), [$2..1000]);

%t Select[Range[250], PrimeQ[DivisorSigma[1, #] + # EulerPhi[#]/2 - 1] &] (* _Michael De Vlieger_, Apr 07 2021 *)

%Y Cf. A083266, A157468, A343151.

%K nonn

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Apr 06 2021