21851557849 has 4 divisors (see below), whose sum is σ = 23838063120. Its totient is φ = 19865052580.

The previous prime is 21851557837. The next prime is 21851557877. The reversal of 21851557849 is 94875515812.

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-21851557849 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 21851557849.

It is not an unprimeable number, because it can be changed into a prime (21851557649) 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, 993252619 + ... + 993252640.

It is an arithmetic number, because the mean of its divisors is an integer number (5959515780).

Almost surely, 2^21851557849 is an apocalyptic number.

It is an amenable number.

21851557849 is a deficient number, since it is larger than the sum of its proper divisors (1986505271).

21851557849 is a wasteful number, since it uses less digits than its factorization.

21851557849 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1986505270.

The product of its digits is 4032000, while the sum is 55.

The spelling of 21851557849 in words is "twenty-one billion, eight hundred fifty-one million, five hundred fifty-seven thousand, eight hundred forty-nine".