6440921 has 4 divisors (see below), whose sum is σ = 6446244. Its totient is φ = 6435600.

The previous prime is 6440893. The next prime is 6440933. The reversal of 6440921 is 1290446.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 384400 + 6056521 = 620^2 + 2461^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6440921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6440821) 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, 131 + ... + 3591.

It is an arithmetic number, because the mean of its divisors is an integer number (1611561).

Almost surely, 2^6440921 is an apocalyptic number.

It is an amenable number.

6440921 is a deficient number, since it is larger than the sum of its proper divisors (5323).

6440921 is a wasteful number, since it uses less digits than its factorization.

6440921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5322.

The product of its (nonzero) digits is 1728, while the sum is 26.

The square root of 6440921 is about 2537.8969640236. The cubic root of 6440921 is about 186.0584180785.

The spelling of 6440921 in words is "six million, four hundred forty thousand, nine hundred twenty-one".