Math - Permutations - Pyramid question

The letters A to O are carved into congruent wooden blocks. Ola is required to stack all the blocks in the shape of a pyramid. An example of one such pyramid is shown below. In how many different ways can this be done?

the pyramid isn't shown. i take it to be 5+4+3+2+1

# of ways = 15c5*10c4*6c3*3c2*1c1 = 37,837,800 <------