Quadrupal Factorials

The so-called quadruple factorial, however, is not the multifactorial n!(4); it is a much larger number given by (2n)!/n!, starting as 1, 2, 12, 120, 1680, 30240, 665280, ... (sequence A001813 in OEIS). It is also equal to

n\equiv 0(\mbox{mod k})

A A A