a(n) = 10^n*(10^n-1)/2.A037182a(n) = 10^n*(10^n-1)/2.Terms a(0) =0a(1) =45a(2) =4950a(3) =499500a(4) =49995000a(5) =4999950000a(6) =499999500000External referencesoeis: A037182