a(n) = 1/2 times the cancellation factor in reducing Sum_{k=0 to 2n+1} 1/k! to lowest terms.

Terms

a(0) =1a(1) =1a(2) =10a(3) =5a(4) =4a(5) =1a(6) =2a(7) =65a(8) =2000a(9) =1a(10) =26a(11) =247a(12) =20a(13) =5a(14) =2a(15) =19a(16) =8a(17) =115a(18) =10a(19) =23a(20) =52a(21) =31a(22) =10a(23) =65a(24) =416a(25) =37a(26) =2a(27) =25a(28) =20a(29) =1