Prove that k.k! = (k+1)! - k! and sum the series 1.1! + 2.2! + 3.3! +...+n.n!

Prove that k.k! = (k+1)! - k! and sum the series 1.1! + 2.2! + 3.3! +...+n.n!

Lyndon chose this as one of his favourite problems. It is accessible but needs some careful analysis of what is included and what is not. A systematic approach is really helpful.

The harmonic triangle is built from fractions with unit numerators using a rule very similar to Pascal's triangle.

How many noughts are at the end of these giant numbers?

Which is larger: (a) 1.000001^{1000000} or 2? (b) 100^{300} or 300! (i.e.factorial 300)

Compares the size of functions f(n) for large values of n.

How many zeros are there at the end of the number which is the product of first hundred positive integers?