6421991 has 8 divisors (see below), whose sum is σ = 6918144. Its totient is φ = 5943960.

The previous prime is 6421967. The next prime is 6421997. The reversal of 6421991 is 1991246.

6421991 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

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 6421991 - 2¹⁸ = 6159847 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 (6421997) 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, 3791 + ... + 5216.

It is an arithmetic number, because the mean of its divisors is an integer number (864768).

Almost surely, 2^6421991 is an apocalyptic number.

6421991 is a deficient number, since it is larger than the sum of its proper divisors (496153).

6421991 is a wasteful number, since it uses less digits than its factorization.

6421991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9061.

The product of its digits is 3888, while the sum is 32.

The square root of 6421991 is about 2534.1647539179. The cubic root of 6421991 is about 185.8759627022.

The spelling of 6421991 in words is "six million, four hundred twenty-one thousand, nine hundred ninety-one".