a(0) = ... = a(4) = 1; a(n) = Sum_{k=0..n-5} Stirling2(n-5,k) * a(k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =2a(8) =5a(9) =15a(10) =52a(11) =203a(12) =878a(13) =4172a(14) =21767a(15) =125536a(16) =809254a(17) =5890115a(18) =48560551a(19) =450859572a(20) =4657423009a(21) =52802518648a(22) =649162712358