1644626681 has 4 divisors (see below), whose sum is σ = 1731186000. Its totient is φ = 1558067364.

The previous prime is 1644626603. The next prime is 1644626713. The reversal of 1644626681 is 1866264461.

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 a de Polignac number, because none of the positive numbers 2^k-1644626681 is a prime.

It is a super-2 number, since 2×1644626681² = 5409593839714151522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1644626281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 43279631 + ... + 43279668.

It is an arithmetic number, because the mean of its divisors is an integer number (432796500).

Almost surely, 2^1644626681 is an apocalyptic number.

It is an amenable number.

1644626681 is a deficient number, since it is larger than the sum of its proper divisors (86559319).

1644626681 is an equidigital number, since it uses as much as digits as its factorization.

1644626681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 86559318.

The product of its digits is 331776, while the sum is 44.

The square root of 1644626681 is about 40553.9971026285. The cubic root of 1644626681 is about 1180.3816349134.

The spelling of 1644626681 in words is "one billion, six hundred forty-four million, six hundred twenty-six thousand, six hundred eighty-one".