Prove by mathematical induction

.1.

n(top) (down)i=0(5i+ 6) =(n+ 1)(5n+ 12)/2.

2. For any integers n4,n!>2n.

3.1 +1/4+1/9++1/n^2 21/n.

4.For any integers 0, 5^(2n+1)+ 2^(2n+1)is divisible by 7.