OFFSET
1,4
LINKS
Eric M. Schmidt, Table of n, a(n) for n = 1..10000
FORMULA
For odd n, a(n) = (n-1)/2.
For n = 2 (mod 4), a(n) = n - 2. - Eric M. Schmidt, Jul 04 2012
EXAMPLE
a(3) = 1 because the group is isomorphic to S_3 and the table is : 1, 1, 1 1,-1, 1 2, 0,-1
MATHEMATICA
a[n_] := Count[FiniteGroupData[{"DihedralGroup", n}, "CharacterTable"], 0, 2]; Array[a, 100] (* Jean-François Alcover, Oct 08 2016 *)
PROG
(Sage)
def A061721(n) :
if n % 2 == 1 : return (n - 1) // 2
if n % 4 == 2 : return n - 2
numzeros = n - 2
np = n // 4
for m in range(1, n // 2) :
t = lcm(m, np)
if (t // np) % 2 == 1 :
maxmul = m * n // 2
numzeros += (maxmul // t) - (maxmul // (2*t))
return numzeros
# Eric M. Schmidt, Jul 04 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
Ahmed Fares (ahmedfares(AT)my-deja.com), Jun 20 2001
EXTENSIONS
More terms from Eric M. Schmidt, Jul 04 2012
STATUS
approved