Polypeptids consist of chemically linked sequences of amino acids. We consider a set of 16 amino acids and sequences of length 7 of these amino acids. An amino acid may appear more than once in a sequence.

1. How many different sequences are there?

2. Half of the amino acids are from the same group A, while the other half are from another group B. The first 4 element(s) of the sequence are all amino acids A, while the remainder are all amino acids B. How many different sequences does it make?

3. How many sequences of length 4 consist of 4 different amino acid(s)?

		1. 5040, 2. 144, 3. 1820
		1. 33232930569601, 2. 144, 3. 1820
		1. 33232930569601, 2. 2097152, 3. 43680
		1. 5040, 2. 2097152, 3. 1820