21720331 has 8 divisors (see below), whose sum is σ = 22297184. Its totient is φ = 21150720.

The previous prime is 21720317. The next prime is 21720371. The reversal of 21720331 is 13302712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21720331 is a prime.

It is a super-2 number, since 2×21720331² = 943545557499122, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21720299 and 21720308.

It is not an unprimeable number, because it can be changed into a prime (21720311) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4555 + ... + 8011.

It is an arithmetic number, because the mean of its divisors is an integer number (2787148).

Almost surely, 2^21720331 is an apocalyptic number.

21720331 is a deficient number, since it is larger than the sum of its proper divisors (576853).

21720331 is a wasteful number, since it uses less digits than its factorization.

21720331 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3621.

The product of its (nonzero) digits is 252, while the sum is 19.

The square root of 21720331 is about 4660.5075903811. The cubic root of 21720331 is about 279.0115272962.

The spelling of 21720331 in words is "twenty-one million, seven hundred twenty thousand, three hundred thirty-one".