OFFSET
1,3
COMMENTS
a(n) <= A213544(n-1) for n >= 2, with equality if and only if n is prime. - Robert Israel, May 10 2019
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
Robert Israel, Plot of a(n)/n^3 for n=3 to 20000
EXAMPLE
MAPLE
MATHEMATICA
A023896[n_] := If[n == 1, 1, (n/2) EulerPhi[n]];
a[n_] := Sum[Boole[GCD[n, k] == 1] A023896[k], {k, 1, n}];
Array[a, 100] (* Jean-François Alcover, Jul 31 2020 *)
PROG
(PARI) s(n) = if(n<2, n>0, n*eulerphi(n)/2); \\ A023896
a(n) = sum(k=1, n, if (gcd(n, k)==1, s(k))); \\ Michel Marcus, May 10 2019
CROSSREFS
KEYWORD
nonn,look
AUTHOR
J. M. Bergot and Robert Israel, May 09 2019
STATUS
approved