721640537 has 4 divisors (see below), whose sum is σ = 744919296. Its totient is φ = 698361780.

The previous prime is 721640503. The next prime is 721640581. The reversal of 721640537 is 735046127.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 735046127 = 2879 ⋅255313.

It is a cyclic number.

It is not a de Polignac number, because 721640537 - 2⁶ = 721640473 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 721640497 and 721640506.

It is not an unprimeable number, because it can be changed into a prime (721640587) 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, 11639333 + ... + 11639394.

It is an arithmetic number, because the mean of its divisors is an integer number (186229824).

Almost surely, 2^721640537 is an apocalyptic number.

It is an amenable number.

721640537 is a deficient number, since it is larger than the sum of its proper divisors (23278759).

721640537 is a wasteful number, since it uses less digits than its factorization.

721640537 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23278758.

The product of its (nonzero) digits is 35280, while the sum is 35.

The square root of 721640537 is about 26863.3679385143. The cubic root of 721640537 is about 896.9611653783.

The spelling of 721640537 in words is "seven hundred twenty-one million, six hundred forty thousand, five hundred thirty-seven".