A053196 Cototients of even numbers.

1, 2, 4, 4, 6, 8, 8, 8, 12, 12, 12, 16, 14, 16, 22, 16, 18, 24, 20, 24, 30, 24, 24, 32, 30, 28, 36, 32, 30, 44, 32, 32, 46, 36, 46, 48, 38, 40, 54, 48, 42, 60, 44, 48, 66, 48, 48, 64, 56, 60, 70, 56, 54, 72, 70, 64, 78, 60, 60, 88, 62, 64, 90, 64, 82, 92, 68, 72, 94, 92, 72, 96

Offset

1,2

Comments

Not all even numbers arise as cototient values: see A005278.

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Formula

a(n) = 2n - phi(2n) = A051953(2n).

Sum_{k=1..n} a(k) ~ c * n^2 / 2, where c = 2 - 8/Pi^2 = 1.1894305... . - Amiram Eldar, Dec 21 2023

Mathematica

Table[(2 n - EulerPhi[2 n]), {n, 1, 80}] (* Vincenzo Librandi, Jul 27 2013 *)

Prog

(PARI) a(n) = 2*n - eulerphi(2*n) \\ Michel Marcus, Jul 26 2013
(Magma) [2*n-EulerPhi(2*n): n in [1..80]]; // Vincenzo Librandi, Jul 28 2013

Crossrefs

Cf. A000010, A051953, A005278.

Sequence in context: A246601 A288529 A288772 * A159634 A186690 A002131

Adjacent sequences: A053193 A053194 A053195 * A053197 A053198 A053199

Keyword

nonn,easy

Author

Labos Elemer, Mar 02 2000

Status

approved