1643981623 has 4 divisors (see below), whose sum is σ = 1649336920. Its totient is φ = 1638626328.

The previous prime is 1643981579. The next prime is 1643981627. The reversal of 1643981623 is 3261893461.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 3261893461 = 1453 ⋅2244937.

It is a cyclic number.

It is not a de Polignac number, because 1643981623 - 2⁹ = 1643981111 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1643981623.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1643981627) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2677188 + ... + 2677801.

It is an arithmetic number, because the mean of its divisors is an integer number (412334230).

Almost surely, 2^1643981623 is an apocalyptic number.

1643981623 is a deficient number, since it is larger than the sum of its proper divisors (5355297).

1643981623 is an equidigital number, since it uses as much as digits as its factorization.

1643981623 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5355296.

The product of its digits is 186624, while the sum is 43.

The square root of 1643981623 is about 40546.0432471530. The cubic root of 1643981623 is about 1180.2272910341.

The spelling of 1643981623 in words is "one billion, six hundred forty-three million, nine hundred eighty-one thousand, six hundred twenty-three".