Problem
ALG-B1-M12-P002 Variant 1, Problem 2
#2
★★☆☆☆ Level 2 of 5
\(u_0=1\), \(u_{n+1}=u_n+2n\). Find \(u_n\).
Sum the differences.
\(u_n=1+\sum_{k=0}^{n-1}2k=1+n(n-1)\).
Mock olympiad problem. Tags: recurrence.