OFFSET
1,2
COMMENTS
a(n) is to A001700 as n!! is to n!.
FORMULA
a(n) = n * (n+2) * ... * ((3*n)-2) / n!!.
EXAMPLE
a(1) = (1)/(1) = 1.
a(2) = (2*4)/(2) = 4.
a(3) = (3*5*7)/(3*1) = 35.
a(4) = (4*6*8*10)/(4*2) = 240.
a(5) = (5*7*9*11*13)/(5*3*1) = 3003.
a(6) = (6*8*10*12*14*16)/(6*4*2) = 26880.
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jonathan Vos Post, Apr 10 2007
EXTENSIONS
Corrected and extended by Klaus Brockhaus, Apr 15 2007
STATUS
approved