721620021 has 8 divisors (see below), whose sum is σ = 995338080. Its totient is φ = 464490992.

The previous prime is 721620017. The next prime is 721620037. The reversal of 721620021 is 120026127.

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

It is a cyclic number.

It is not a de Polignac number, because 721620021 - 2² = 721620017 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 721620021.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721620121) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4147155 + ... + 4147328.

It is an arithmetic number, because the mean of its divisors is an integer number (124417260).

Almost surely, 2^721620021 is an apocalyptic number.

It is an amenable number.

721620021 is a deficient number, since it is larger than the sum of its proper divisors (273718059).

721620021 is a wasteful number, since it uses less digits than its factorization.

721620021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8294515.

The product of its (nonzero) digits is 336, while the sum is 21.

The square root of 721620021 is about 26862.9860775008. The cubic root of 721620021 is about 896.9526651954.

Adding to 721620021 its reverse (120026127), we get a palindrome (841646148).

The spelling of 721620021 in words is "seven hundred twenty-one million, six hundred twenty thousand, twenty-one".