1645213221 has 16 divisors (see below), whose sum is σ = 2438092800. Its totient is φ = 1096475904.

The previous prime is 1645213169. The next prime is 1645213231. The reversal of 1645213221 is 1223125461.

1645213221 is a `hidden beast` number, since 1 + 645 + 2 + 13 + 2 + 2 + 1 = 666.

1645213221 is digitally balanced in base 4, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 1645213221 - 2⁷ = 1645213093 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1645213231) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 108700 + ... + 122906.

It is an arithmetic number, because the mean of its divisors is an integer number (152380800).

Almost surely, 2^1645213221 is an apocalyptic number.

It is an amenable number.

1645213221 is a deficient number, since it is larger than the sum of its proper divisors (792879579).

1645213221 is a wasteful number, since it uses less digits than its factorization.

1645213221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18505 (or 18499 counting only the distinct ones).

The product of its digits is 2880, while the sum is 27.

The square root of 1645213221 is about 40561.2280509355. The cubic root of 1645213221 is about 1180.5219420852.

Adding to 1645213221 its reverse (1223125461), we get a palindrome (2868338682).

The spelling of 1645213221 in words is "one billion, six hundred forty-five million, two hundred thirteen thousand, two hundred twenty-one".