1644642121 has 4 divisors (see below), whose sum is σ = 1645347600. Its totient is φ = 1643936644.

The previous prime is 1644642107. The next prime is 1644642137. The reversal of 1644642121 is 1212464461.

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 1644642121 - 2¹⁹ = 1644117833 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1644642151) 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, 349231 + ... + 353908.

It is an arithmetic number, because the mean of its divisors is an integer number (411336900).

Almost surely, 2^1644642121 is an apocalyptic number.

It is an amenable number.

1644642121 is a deficient number, since it is larger than the sum of its proper divisors (705479).

1644642121 is an equidigital number, since it uses as much as digits as its factorization.

1644642121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 705478.

The product of its digits is 9216, while the sum is 31.

The square root of 1644642121 is about 40554.1874656613. The cubic root of 1644642121 is about 1180.3853287680.

The spelling of 1644642121 in words is "one billion, six hundred forty-four million, six hundred forty-two thousand, one hundred twenty-one".