a(n) = 10^n*(10^n+1)/2.A037156a(n) = 10^n*(10^n+1)/2.Terms a(0) =1a(1) =55a(2) =5050a(3) =500500a(4) =50005000a(5) =5000050000a(6) =500000500000External referencesoeis: A037156