The next highly composite number is 6. Four is the second square number, the second centered triangular number. Of course, there are four sides to the square as well as four vertices, analogous to the four corners of a room.4 is the smallest squared prime (p 2) and the only even number in this form.It has an aliquot sum of 3 which is itself prime. The aliquot sequence of 4 has 4 members (4, 3, 1, 0) and is accordingly the first member of the 3-aliquot tree.he next highly composite number is 6. Four is the second square number, the second centered triangular number. Of course, there are four sides to the square as well as four vertices, analogous to the four corners of a room.