21851887205 has 4 divisors (see below), whose sum is σ = 26222264652. Its totient is φ = 17481509760.

The previous prime is 21851887177. The next prime is 21851887223. The reversal of 21851887205 is 50278815812.

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 13267123489 + 8584763716 = 115183^2 + 92654^2 .

It is not a de Polignac number, because 21851887205 - 2¹⁰ = 21851886181 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 21851887205.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2185188716 + ... + 2185188725.

It is an arithmetic number, because the mean of its divisors is an integer number (6555566163).

Almost surely, 2^21851887205 is an apocalyptic number.

It is an amenable number.

21851887205 is a deficient number, since it is larger than the sum of its proper divisors (4370377447).

21851887205 is an equidigital number, since it uses as much as digits as its factorization.

21851887205 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4370377446.

The product of its (nonzero) digits is 358400, while the sum is 47.

The spelling of 21851887205 in words is "twenty-one billion, eight hundred fifty-one million, eight hundred eighty-seven thousand, two hundred five".