OFFSET
1,4
LINKS
Michael De Vlieger, Table of n, a(n) for n = 1..10000
FORMULA
a(n) = cototient(2n+1) = A051953(2n+1).
Sum_{k=1..n} a(k) ~ c * n^2, where c = 1 - 8/Pi^2. - Amiram Eldar, Dec 15 2023
EXAMPLE
n=12, 2n+1=25, phi(25)=20, cototient(25)=25-20=5, a(12)=5.
n=16, 2n+1=33, phi(33)=20, cototient(33)=33-20=13, a(16)=13.
MATHEMATICA
Table[# - EulerPhi@ # &[2 n + 1], {n, 84}] (* Michael De Vlieger, Aug 15 2017 *)
PROG
(PARI) A053193(n) = { 2*n+1 - eulerphi(2*n+1)} \\ Michel Marcus, Jul 26 2013
(Magma) [2*n+1-EulerPhi(2*n+1): n in [1..90]]; // Vincenzo Librandi, Aug 16 2017
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Labos Elemer, Mar 02 2000
STATUS
approved