OFFSET
1,2
COMMENTS
A119347(n) <= a(n). - Reinhard Zumkeller, Jun 27 2015
LINKS
Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Wasin So, Integral circulant graphs, Discr. Math. 306 (1) (2006) 153-158
FORMULA
a(n) = -1 + 2^tau(n), where tau(n) = DivisorSigma(0, n) = A000005(n).
EXAMPLE
For all prime numbers p, a(p)=3, since those subsets are {{1,p},{1},{p}}.
MAPLE
MATHEMATICA
Table[2^DivisorSigma[0, n] - 1, {n, 73}] (* Michael De Vlieger, Dec 11 2015 *)
PROG
(PARI) a(n) = 2^(numdiv(n)) - 1; \\ Michel Marcus, Dec 15 2013
(Haskell)
a100587 = (subtract 1) . (2 ^) . a000005'
-- Reinhard Zumkeller, Jun 27 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Labos Elemer, Dec 01 2004
STATUS
approved