6421720591 has 24 divisors (see below), whose sum is σ = 7763378112. Its totient is φ = 5274139200.

The previous prime is 6421720549. The next prime is 6421720609. The reversal of 6421720591 is 1950271246.

It is not a de Polignac number, because 6421720591 - 2¹⁵ = 6421687823 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 6421720591.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6421720511) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 30501 + ... + 117361.

It is an arithmetic number, because the mean of its divisors is an integer number (323474088).

Almost surely, 2^6421720591 is an apocalyptic number.

6421720591 is a deficient number, since it is larger than the sum of its proper divisors (1341657521).

6421720591 is a wasteful number, since it uses less digits than its factorization.

6421720591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86943 (or 86932 counting only the distinct ones).

The product of its (nonzero) digits is 30240, while the sum is 37.

The square root of 6421720591 is about 80135.6387071320. The cubic root of 6421720591 is about 1858.7335378967.

The spelling of 6421720591 in words is "six billion, four hundred twenty-one million, seven hundred twenty thousand, five hundred ninety-one".