21123533551 has 4 divisors (see below), whose sum is σ = 21130078600. Its totient is φ = 21116988504.

The previous prime is 21123533491. The next prime is 21123533573. The reversal of 21123533551 is 15533532112.

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 21123533551 - 2²⁹ = 20586662639 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 (21123533591) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3267681 + ... + 3274138.

It is an arithmetic number, because the mean of its divisors is an integer number (5282519650).

Almost surely, 2^21123533551 is an apocalyptic number.

21123533551 is a deficient number, since it is larger than the sum of its proper divisors (6545049).

21123533551 is an equidigital number, since it uses as much as digits as its factorization.

21123533551 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6545048.

The product of its digits is 13500, while the sum is 31.

The spelling of 21123533551 in words is "twenty-one billion, one hundred twenty-three million, five hundred thirty-three thousand, five hundred fifty-one".