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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 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=1..56.

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: A187791 A245235 A151924 * A058524 A072576 A271342

Adjacent sequences:  A268339 A268340 A268341 * A268343 A268344 A268345

KEYWORD

nonn

AUTHOR

Michel Marcus, Feb 02 2016

STATUS

approved

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Last modified October 22 10:35 EDT 2018. Contains 316436 sequences. (Running on oeis4.)