1644158921 has 4 divisors (see below), whose sum is σ = 1654004352. Its totient is φ = 1634313492.

The previous prime is 1644158909. The next prime is 1644158941. The reversal of 1644158921 is 1298514461.

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 1644158921 - 2¹⁴ = 1644142537 is a prime.

It is a super-3 number, since 3×1644158921³ (a number of 29 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1644158941) 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, 4922465 + ... + 4922798.

It is an arithmetic number, because the mean of its divisors is an integer number (413501088).

Almost surely, 2^1644158921 is an apocalyptic number.

It is an amenable number.

1644158921 is a deficient number, since it is larger than the sum of its proper divisors (9845431).

1644158921 is an equidigital number, since it uses as much as digits as its factorization.

1644158921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9845430.

The product of its digits is 69120, while the sum is 41.

The square root of 1644158921 is about 40548.2295667764. The cubic root of 1644158921 is about 1180.2697173835.

The spelling of 1644158921 in words is "one billion, six hundred forty-four million, one hundred fifty-eight thousand, nine hundred twenty-one".