MathDB

9

Part of 2015 Online Math Open Problems

Problems(2)

2014-2015 Spring OMO #9

Source:

4/14/2015
Find the sum of the decimal digits of the number 5∑k=199k(k+1)(k2+k+1). 5\sum_{k=1}^{99} k(k + 1)(k^2 + k + 1). Proposed by Robin Park
Online Math Open
2015-2016 Fall OMO #9

Source:

11/18/2015
Let s1,s2,…s_1, s_2, \dots be an arithmetic progression of positive integers. Suppose that s_{s_1} = x+2,   s_{s_2} = x^2+18,  \text{and}  s_{s_3} = 2x^2+18. Determine the value of xx.
Proposed by Evan Chen
Online Math Open