OFFSET
1,3
LINKS
Eric Weisstein's World of Mathematics, Complete Graph
Eric Weisstein's World of Mathematics, Minimum Edge Cover
FORMULA
a(n) = (n - 1)!! for n == 0 (mod 2).
a(n) = 2^((1 - n)/2)*n!/Gamma((n - 1)/2) for n == 1 (mod 2).
a(1) = 0, a(2) = 1, a(n) = (n - 1)*(((n - 2)*(n - 1)*n - 4)*a(n - 2) - 6*a(n - 1))/(n*(11 + (n - 6)*n) - 10).
MATHEMATICA
Table[Piecewise[{{(2^((1 - n)/2) Gamma[n + 1])/Gamma[(n - 1)/2], Mod[n, 2] == 1}, {(n - 1)!!, Mod[n, 2] == 0}}, 0], {n, 20}]
RecurrenceTable[{a[1] == 0, a[2] == 1, a[n] == ((n - 1) (((n - 2) (n - 1) n - 4) a[n - 2] - 6 a[n - 1]))/(n (11 + (n - 6) n) - 10)}, a, {n, 20}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Eric W. Weisstein, Feb 27 2022
STATUS
approved