MathDB
Sprind Round (2012) #1

Source:

December 3, 2012
arithmetic sequence

Problem Statement

Let {an}n=1 \{a_n\}_{n=1}^\infty be an arithmetic progression with a1>0 a_1 > 0 and 5a13=6a19 5\cdot a_{13} = 6\cdot a_{19} . What is the smallest integer n n such that an<0 a_n<0 ?