721663537 has 8 divisors (see below), whose sum is σ = 826914816. Its totient is φ = 616951392.

The previous prime is 721663451. The next prime is 721663543. The reversal of 721663537 is 735366127.

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 721663537 - 2⁷ = 721663409 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 721663537.

It is not an unprimeable number, because it can be changed into a prime (721663037) 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, 131908 + ... + 137269.

It is an arithmetic number, because the mean of its divisors is an integer number (103364352).

Almost surely, 2^721663537 is an apocalyptic number.

It is an amenable number.

721663537 is a deficient number, since it is larger than the sum of its proper divisors (105251279).

721663537 is a wasteful number, since it uses less digits than its factorization.

721663537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 269567.

The product of its digits is 158760, while the sum is 40.

The square root of 721663537 is about 26863.7960273674. The cubic root of 721663537 is about 896.9706945398.

The spelling of 721663537 in words is "seven hundred twenty-one million, six hundred sixty-three thousand, five hundred thirty-seven".