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A053196
Cototients of even numbers.
1
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
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
KEYWORD
nonn,easy
AUTHOR
Labos Elemer, Mar 02 2000
STATUS
approved