Question

求1.3.6.10.15……的通项公式

Answer 1

a1=1,a2=a1+2,a3=a2+3……an=an-1 + n

an - an-1 = n

an = an - an-1 + an-1 - an-2 + …… + a2 - a1 + a1

= n + n-1 + n-2 + …… + 1

= n(n+1)/2