1644243857 has 4 divisors (see below), whose sum is σ = 1675267380. Its totient is φ = 1613220336.

The previous prime is 1644243833. The next prime is 1644243863. The reversal of 1644243857 is 7583424461.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1411955776 + 232288081 = 37576^2 + 15241^2 .

It is a cyclic number.

It is not a de Polignac number, because 1644243857 - 2²² = 1640049553 is a prime.

It is a super-3 number, since 3×1644243857³ (a number of 29 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1644243257) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15511682 + ... + 15511787.

It is an arithmetic number, because the mean of its divisors is an integer number (418816845).

Almost surely, 2^1644243857 is an apocalyptic number.

It is an amenable number.

1644243857 is a deficient number, since it is larger than the sum of its proper divisors (31023523).

1644243857 is an equidigital number, since it uses as much as digits as its factorization.

1644243857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 31023522.

The product of its digits is 645120, while the sum is 44.

The square root of 1644243857 is about 40549.2768986082. The cubic root of 1644243857 is about 1180.2900409790.

The spelling of 1644243857 in words is "one billion, six hundred forty-four million, two hundred forty-three thousand, eight hundred fifty-seven".