What is the tetrahedral number for the 5th layer?

if the numbers are 1,4,10,20,35What is the tetrahedral number for the 5th layer?
take a look at Pascal's Triangle:





1...1


1...2...1


1...3...3...1


1...4...6...4...1


1...5..10..10...5...1


1...6..15..20..15...6...1


1...7..21..35..35..21...7...1


1...8..28..56..70..56..28...8...1





You see how your tetrahedal numbers are in the fourth column? Just follow it down to whatever you mean by ';5th layer.'; These numbers can be computed directly as nC3 on a TI-83.