221. If the counting numbers are written in order, what is the value of the 2015th digit written?
227. A sequence begins 1, 2, …, and each term after the second term is the sum of all
preceding terms. What is the 15th term of this sequence?
227. 1,2,3,6 --------
nth term = (n-1)(n)/2
hence 15th term = 14*15/2 = 105
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