1643998861 has 4 divisors (see below), whose sum is σ = 1670949724. Its totient is φ = 1617048000.

The previous prime is 1643998859. The next prime is 1643998901. The reversal of 1643998861 is 1688993461.

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 356983236 + 1287015625 = 18894^2 + 35875^2 .

It is a cyclic number.

It is not a de Polignac number, because 1643998861 - 2¹ = 1643998859 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 (1643998841) 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, 13475340 + ... + 13475461.

It is an arithmetic number, because the mean of its divisors is an integer number (417737431).

Almost surely, 2^1643998861 is an apocalyptic number.

It is an amenable number.

1643998861 is a deficient number, since it is larger than the sum of its proper divisors (26950863).

1643998861 is an equidigital number, since it uses as much as digits as its factorization.

1643998861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26950862.

The product of its digits is 2239488, while the sum is 55.

The square root of 1643998861 is about 40546.2558197425. The cubic root of 1643998861 is about 1180.2314161181.

The spelling of 1643998861 in words is "one billion, six hundred forty-three million, nine hundred ninety-eight thousand, eight hundred sixty-one".