A362334 - OEIS

%I #17 May 28 2023 13:25:20

%S 3,3,6,4,10,6,12,8,16,8,22,10,20,14,24,14,34,14,30,18,34,18,42,20,38,

%T 24,46,20,58,24,50,32,44,28,60,30,60,34,64,28,82,32,66,42,70,38,88,36,

%U 74,44,84,42,92,42,76,52,94,44,118,46,96,62,84,52,114,52,110

%N a(n) = A000010(n) + A000010(n+2), where A000010 is the Euler phi-function.

%C Conjecture: a(2*n) <= a(2*n-1) and a(2*n) < a(2*n+1).

%F a(n) = phi(n) + phi(n+2).

%e For n = 3, phi(3) = 2 and phi(5) = 4, so a(3) = 6.

%t a[n_] := Plus @@ EulerPhi[n + {0, 2}]; Array[a, 100] (* _Amiram Eldar_, Apr 18 2023 *)

%o (PARI) a(n) = eulerphi(n) + eulerphi(n+2); \\ _Michel Marcus_, Apr 17 2023

%Y Cf. A000010, A092404.

%K nonn

%O 1,1

%A _Alexandre Herrera_, Apr 16 2023