等差是列的通项式an=a1+(n-1)d (d为公差)
等差是列的前n项和:Sn=na1+n(n-1)d/2
等比是列的通项式an=a1*q^(n-1) (q为公比)
等比数列的前n项和:Sn=[a1(1-q^n)]/(1-q)