This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A266990 #29 Oct 09 2021 06:56:48
%S A266990 2,4,5,9,15,17,20,22,23,27,28,31,32,34,36,38,39,41,43,46,47,49,52,54,
%T A266990 56,58,61,64,67,69,72,73,76,81,83,85,86,90,91,92,93,95,96,99,101,103,
%U A266990 105,107,109,111,118,120,125,128,129,131,132,133,138,141,143,144,146,150
%N A266990 The indices of primes p for which the average of the primitive roots is > p/2.
%C A266990 It appears that these primes are all congruent to 3 (mod 4).
%H A266990 Amiram Eldar, <a href="/A266990/b266990.txt">Table of n, a(n) for n = 1..10000</a>
%F A266990 a(n) = A000720(A267009(n)). - _Amiram Eldar_, Oct 09 2021
%e A266990 a(2) = 4 is a term since prime(a(2)) = prime(4) = 7, the primitive roots of 7 are 3 and 5 and their average is (3+5)/2 = 8/2 > 7/2.
%t A266990 A = Table[Total[Flatten[Position[Table[MultiplicativeOrder[i, Prime[k]], {i, Prime[k] - 1}],Prime[k] - 1]]]/(EulerPhi[Prime[k] - 1] Prime[k]/2), {k, 1, 1000}]; Flatten[Position[A, _?(# > 1 &)]]
%t A266990 Select[Range[150], Mean[PrimitiveRootList[(p = Prime[#])]] > p/2 &] (* _Amiram Eldar_, Oct 09 2021 *)
%Y A266990 Cf. A000720, A008330, A060749, A088144, A267009.
%K A266990 nonn
%O A266990 1,1
%A A266990 _Dimitri Papadopoulos_, Jan 08 2016