21044243251 has 4 divisors (see below), whose sum is σ = 21400925400. Its totient is φ = 20687561104.

The previous prime is 21044243249. The next prime is 21044243263. The reversal of 21044243251 is 15234244012.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21044243251 - 2¹ = 21044243249 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21044243201) 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, 178340986 + ... + 178341103.

It is an arithmetic number, because the mean of its divisors is an integer number (5350231350).

Almost surely, 2^21044243251 is an apocalyptic number.

21044243251 is a deficient number, since it is larger than the sum of its proper divisors (356682149).

21044243251 is an equidigital number, since it uses as much as digits as its factorization.

21044243251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 356682148.

The product of its (nonzero) digits is 7680, while the sum is 28.

Adding to 21044243251 its reverse (15234244012), we get a palindrome (36278487263).

The spelling of 21044243251 in words is "twenty-one billion, forty-four million, two hundred forty-three thousand, two hundred fifty-one".