721637691 has 4 divisors (see below), whose sum is σ = 962183592. Its totient is φ = 481091792.

The previous prime is 721637663. The next prime is 721637701. The reversal of 721637691 is 196736127.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 721637691 - 2⁵ = 721637659 is a prime.

It is a super-2 number, since 2×721637691² = 1041521914143622962, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (721633691) 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, 120272946 + ... + 120272951.

It is an arithmetic number, because the mean of its divisors is an integer number (240545898).

Almost surely, 2^721637691 is an apocalyptic number.

721637691 is a deficient number, since it is larger than the sum of its proper divisors (240545901).

721637691 is a wasteful number, since it uses less digits than its factorization.

721637691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 240545900.

The product of its digits is 95256, while the sum is 42.

The square root of 721637691 is about 26863.3149666976. The cubic root of 721637691 is about 896.9599862341.

The spelling of 721637691 in words is "seven hundred twenty-one million, six hundred thirty-seven thousand, six hundred ninety-one".