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 A363700 #17 Jun 20 2023 06:33:27 %S A363700 4,6,10,8,22,18,24,24,46,58,36,40,82,56,72,106,96,80,72,120,84,104, %T A363700 166,178,96,168,132,168,144,226,128,262,200,180,264,200,144,216,264, %U A363700 346,358,220,382,252,312,216,276,296,288,288,466,478,264,502,408,480,420,360,288,562 %N A363700 a(n) = phi(2*prime(n)+1). %C A363700 2*prime(n)+1 is prime iff a(n) = 2*prime(n). %F A363700 a(n) = A000010(A072055(n)). %F A363700 a(n) = A037225(A000040(n)). %t A363700 a[n_] := EulerPhi[2*Prime[n] + 1]; Array[a, 100] (* _Amiram Eldar_, Jun 16 2023 *) %o A363700 (PARI) a(n)=eulerphi(2*prime(n)+1) %Y A363700 Cf. A000010, A000040, A008331, A037225, A072055. %K A363700 nonn %O A363700 1,1 %A A363700 _Alain Rocchelli_, Jun 16 2023