66721656 has 64 divisors (see below), whose sum is σ = 172586880. Its totient is φ = 21479040.

The previous prime is 66721639. The next prime is 66721657. The reversal of 66721656 is 65612766.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66721657) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 201411 + ... + 201741.

It is an arithmetic number, because the mean of its divisors is an integer number (2696670).

Almost surely, 2^66721656 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 66721656, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (86293440).

66721656 is an abundant number, since it is smaller than the sum of its proper divisors (105865224).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

66721656 is a wasteful number, since it uses less digits than its factorization.

66721656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 604 (or 600 counting only the distinct ones).

The product of its digits is 90720, while the sum is 39.

The square root of 66721656 is about 8168.3325103720. The cubic root of 66721656 is about 405.5915878107.

The spelling of 66721656 in words is "sixty-six million, seven hundred twenty-one thousand, six hundred fifty-six".