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 A094051 #11 Jan 12 2024 01:27:31 %S A094051 1,1,2,2,4,3,5,6,4,6,8,6,11,12,14,8,10,12,12,12,20,20,16,20,16,26,18, %T A094051 24,18,24,32,22,36,20,24,27,41,42,44,24,36,32,42,30,24,36,56,36,56,48, %U A094051 32,50,64,65,66,36,44,48,46,72,48,60,48,78,40,48,86,56,80,89,60,60,54,95,96,60 %N A094051 a(n) = phi(phi(p))/2 where p = prime(n). %C A094051 Offset is 3 as a(1) and a(2) would be fractional. - _Michel Marcus_, Aug 13 2013 %H A094051 Amiram Eldar, <a href="/A094051/b094051.txt">Table of n, a(n) for n = 3..10000</a> %F A094051 From _Amiram Eldar_, Jan 12 2024: (Start) %F A094051 a(n) = A008330(n)/2. %F A094051 a(n) = A023022(A000040(n)-1). (End) %t A094051 EulerPhi[Prime[Range[3, 100]] - 1]/2 (* _Amiram Eldar_, Jan 12 2024 *) %o A094051 (PARI) a(n) = eulerphi(eulerphi(prime(n)))/2; \\ _Michel Marcus_, Aug 13 2013 %Y A094051 Cf. A000010, A000040, A008330, A023022. %K A094051 nonn,easy %O A094051 3,3 %A A094051 _Matthijs Coster_, Apr 29 2004