10! (read ten factorial)
Applying the binomal theorem, multiply all the digits.1x2x3x4x5x6x7x8x9x10.You probably need to practise arithmetic more than I do.
Taken individually, 1, 2, 3, 5 and 7 don't have prime factorizations. That leaves2 x 2 = 42 x 3 = 62 x 2 x 2 = 83 x 3 = 92 x 5 = 10Collectively, 28 x 34 x 52 x 7 = 3,628,800