4).…Ã2Å⇔N(N+1) + 1⇔N(N+1) + 1N+12N+2 <N+2 <N+1

4).…ã

2

Å⇔n(n+1) + 1⇔n(n+1) + 1n+12n+2 <n+2 <n+1