21651005549 has 4 divisors (see below), whose sum is σ = 21651824220. Its totient is φ = 21650186880.

The previous prime is 21651005543. The next prime is 21651005591. The reversal of 21651005549 is 94550015612.

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 13579240900 + 8071764649 = 116530^2 + 89843^2 .

It is a cyclic number.

It is not a de Polignac number, because 21651005549 - 2¹⁶ = 21650940013 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21651005543) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 368294 + ... + 423015.

It is an arithmetic number, because the mean of its divisors is an integer number (5412956055).

Almost surely, 2^21651005549 is an apocalyptic number.

It is an amenable number.

21651005549 is a deficient number, since it is larger than the sum of its proper divisors (818671).

21651005549 is an equidigital number, since it uses as much as digits as its factorization.

21651005549 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 818670.

The product of its (nonzero) digits is 54000, while the sum is 38.

The spelling of 21651005549 in words is "twenty-one billion, six hundred fifty-one million, five thousand, five hundred forty-nine".