721690021 has 8 divisors (see below), whose sum is σ = 810996480. Its totient is φ = 637210992.

The previous prime is 721690019. The next prime is 721690049. The reversal of 721690021 is 120096127.

It is a happy number.

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 721690021 - 2¹ = 721690019 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721690051) 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, 1206541 + ... + 1207138.

It is an arithmetic number, because the mean of its divisors is an integer number (101374560).

Almost surely, 2^721690021 is an apocalyptic number.

It is an amenable number.

721690021 is a deficient number, since it is larger than the sum of its proper divisors (89306459).

721690021 is a wasteful number, since it uses less digits than its factorization.

721690021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2413715.

The product of its (nonzero) digits is 1512, while the sum is 28.

The square root of 721690021 is about 26864.2889539254. The cubic root of 721690021 is about 896.9816669113.

The spelling of 721690021 in words is "seven hundred twenty-one million, six hundred ninety thousand, twenty-one".