1645921 has 4 divisors (see below), whose sum is σ = 1649200. Its totient is φ = 1642644.

The previous prime is 1645909. The next prime is 1645927. The reversal of 1645921 is 1295461.

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.

It is a cyclic number.

It is not a de Polignac number, because 1645921 - 2⁹ = 1645409 is a prime.

It is a Duffinian number.

1645921 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 1645921.

It is not an unprimeable number, because it can be changed into a prime (1645927) 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, 711 + ... + 1948.

It is an arithmetic number, because the mean of its divisors is an integer number (412300).

2^1645921 is an apocalyptic number.

It is an amenable number.

1645921 is a deficient number, since it is larger than the sum of its proper divisors (3279).

1645921 is an equidigital number, since it uses as much as digits as its factorization.

1645921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3278.

The product of its digits is 2160, while the sum is 28.

The square root of 1645921 is about 1282.9345267784. The cubic root of 1645921 is about 118.0691206640.

The spelling of 1645921 in words is "one million, six hundred forty-five thousand, nine hundred twenty-one".