a(n) = (n-p_1)(n-p_2)...(n-p_k) where p_k is the k-th prime and is also the largest prime < n.

Terms

a(0) =1a(1) =1a(2) =1a(3) =2a(4) =6a(5) =12a(6) =40a(7) =90a(8) =336a(9) =840a(10) =1728a(11) =3150a(12) =10560a(13) =24948a(14) =99840a(15) =270270a(16) =604800a(17) =1201200a(18) =4386816a(19) =11277630a(20) =49029120a(21) =143896500a(22) =348364800a(23) =746876130a(24) =2937876480a(25) =8117240040a(26) =18923520000a(27) =39628338750a(28) =76859228160a(29) =140548508100