Smallest n-digit triangular number.

Terms

a(0) =1a(1) =10a(2) =105a(3) =1035a(4) =10011a(5) =100128a(6) =1000405a(7) =10001628a(8) =100005153a(9) =1000006281a(10) =10000020331a(11) =100000404505