Double subfactorials: a(n) = (-1)^floor(n/2) * n!! * Sum_{i=0..floor(n/2)} (-1)^i/(n-2*i)!!.

A334578

Double subfactorials: a(n) = (-1)^floor(n/2) * n!! * Sum_{i=0..floor(n/2)} (-1)^i/(n-2*i)!!.

Terms

    a(0) =1a(1) =1a(2) =1a(3) =2a(4) =5a(5) =11a(6) =29a(7) =76a(8) =233a(9) =685a(10) =2329a(11) =7534a(12) =27949a(13) =97943a(14) =391285a(15) =1469144a(16) =6260561a(17) =24975449a(18) =112690097a(19) =474533530a(20) =2253801941a(21) =9965204131a(22) =49583642701a(23) =229199695012

External references