66720831 has 4 divisors (see below), whose sum is σ = 88961112. Its totient is φ = 44480552.

The previous prime is 66720751. The next prime is 66720889. The reversal of 66720831 is 13802766.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 66720831 - 2¹⁸ = 66458687 is a prime.

It is a super-2 number, since 2×66720831² = 8903338578661122, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 66720792 and 66720801.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66720431) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 11120136 + ... + 11120141.

It is an arithmetic number, because the mean of its divisors is an integer number (22240278).

Almost surely, 2^66720831 is an apocalyptic number.

66720831 is a deficient number, since it is larger than the sum of its proper divisors (22240281).

66720831 is a wasteful number, since it uses less digits than its factorization.

66720831 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22240280.

The product of its (nonzero) digits is 12096, while the sum is 33.

The square root of 66720831 is about 8168.2820103128. The cubic root of 66720831 is about 405.5899161174.

The spelling of 66720831 in words is "sixty-six million, seven hundred twenty thousand, eight hundred thirty-one".