720688421 has 4 divisors (see below), whose sum is σ = 725461344. Its totient is φ = 715915500.

The previous prime is 720688399. The next prime is 720688427. The reversal of 720688421 is 124886027.

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: 124886027 = 7 ⋅17840861.

It is a cyclic number.

It is not a de Polignac number, because 720688421 - 2⁶ = 720688357 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 (720688427) 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, 2386235 + ... + 2386536.

It is an arithmetic number, because the mean of its divisors is an integer number (181365336).

Almost surely, 2^720688421 is an apocalyptic number.

It is an amenable number.

720688421 is a deficient number, since it is larger than the sum of its proper divisors (4772923).

720688421 is a wasteful number, since it uses less digits than its factorization.

720688421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4772922.

The product of its (nonzero) digits is 43008, while the sum is 38.

The square root of 720688421 is about 26845.6406330711. The cubic root of 720688421 is about 896.5665150891.

The spelling of 720688421 in words is "seven hundred twenty million, six hundred eighty-eight thousand, four hundred twenty-one".