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A268342
Number of edges in the unitary addition Cayley graph Gn.
0
0, 2, 2, 8, 8, 12, 18, 32, 24, 40, 50, 48, 72, 84, 56, 128, 128, 108, 162, 160, 120, 220, 242, 192, 240, 312, 234, 336, 392, 240, 450, 512, 320, 544, 408, 432, 648, 684, 456, 640, 800, 504, 882, 880, 528, 1012, 1058, 768, 1008, 1000, 800, 1248, 1352, 972, 1080, 1344
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
Cf. A268341.
Sequence in context: A151924 A346205 A343984 * A058524 A072576 A271342
KEYWORD
nonn
AUTHOR
Michel Marcus, Feb 02 2016
STATUS
approved