Second order complementary Bell numbers.

Terms

a(0) =1a(1) =-1a(2) =2a(3) =-4a(4) =9a(5) =-22a(6) =54a(7) =-139a(8) =372a(9) =-948a(10) =2607a(11) =-7388a(12) =16058a(13) =-58957a(14) =174854a(15) =210448a(16) =4345025a(17) =-2008714a(18) =-165872030a(19) =-1756557123a(20) =-6144936528a(21) =60244093040