670446201600domain: NAppears in sequencesa(n) = 1*2*3*4*5*6*7*8*9*10 + 11*12*13*14*15*16*17*18*19*20 + 21*22*23*24*25*26*27*28*29*30 + ... + (up to n).at n=19A319212a(n) = 10*9*8*7*6*5*4*3*2*1 + 20*19*18*17*16*15*14*13*12*11 + ... + (up to the n-th term).at n=19A319874