OFFSET
1,2
COMMENTS
For n>1, the unitary addition Cayley graph Gn is the graph whose vertices are Z/nZ and where 2 vertices x and y are adjacent if x+y is a unit in Z/nZ.
FORMULA
a(n) = n*phi(n) if n is even, (n-1)*phi(n)/2 if n is odd.
MATHEMATICA
Table[If[EvenQ@ n, n EulerPhi[n], (n - 1) EulerPhi[n]/2], {n, 56}] (* Michael De Vlieger, Feb 02 2016 *)
PROG
(PARI) a(n) = if (n % 2, eulerphi(n)*(n-1)/2, eulerphi(n)*n);
(Magma) [IsOdd(n mod 2) select (n-1)*(EulerPhi(n))/2 else n*(EulerPhi(n)): n in [1..52]]; // Vincenzo Librandi, Feb 03 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Feb 02 2016
STATUS
approved