Index of largest triangular number with n digits.

Terms

a(0) =3a(1) =13a(2) =44a(3) =140a(4) =446a(5) =1413a(6) =4471a(7) =14141a(8) =44720a(9) =141420a(10) =447213a(11) =1414213a(12) =4472135a(13) =14142135a(14) =44721359a(15) =141421355a(16) =447213594a(17) =1414213561a(18) =4472135954a(19) =14142135623a(20) =44721359549a(21) =141421356236a(22) =447213595499