1643885813 has 4 divisors (see below), whose sum is σ = 1645160448. Its totient is φ = 1642611180.

The previous prime is 1643885809. The next prime is 1643885819. The reversal of 1643885813 is 3185883461.

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 1643885813 - 2² = 1643885809 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1643885819) 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, 635381 + ... + 637962.

It is an arithmetic number, because the mean of its divisors is an integer number (411290112).

Almost surely, 2^1643885813 is an apocalyptic number.

It is an amenable number.

1643885813 is a deficient number, since it is larger than the sum of its proper divisors (1274635).

1643885813 is a wasteful number, since it uses less digits than its factorization.

1643885813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1274634.

The product of its digits is 552960, while the sum is 47.

The square root of 1643885813 is about 40544.8617336402. The cubic root of 1643885813 is about 1180.2043630054.

The spelling of 1643885813 in words is "one billion, six hundred forty-three million, eight hundred eighty-five thousand, eight hundred thirteen".