a(n) = number of n-digit terms in A108571.

Terms

a(0) =1a(1) =1a(2) =4a(3) =5a(4) =16a(5) =82a(6) =169a(7) =541a(8) =2272a(9) =17965a(10) =44407a(11) =201751a(12) =801515a(13) =4890886a(14) =52218595a(15) =165519640a(16) =835947970a(17) =4290442728a(18) =24096524166a(19) =179566203960