21533312551 has 4 divisors (see below), whose sum is σ = 22275840600. Its totient is φ = 20790784504.

The previous prime is 21533312533. The next prime is 21533312611. The reversal of 21533312551 is 15521333512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21533312551 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 (21533312051) 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, 371263981 + ... + 371264038.

It is an arithmetic number, because the mean of its divisors is an integer number (5568960150).

Almost surely, 2^21533312551 is an apocalyptic number.

21533312551 is a deficient number, since it is larger than the sum of its proper divisors (742528049).

21533312551 is an equidigital number, since it uses as much as digits as its factorization.

21533312551 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 742528048.

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

It can be divided in two parts, 21533 and 312551, that added together give a square (334084 = 578²).

The spelling of 21533312551 in words is "twenty-one billion, five hundred thirty-three million, three hundred twelve thousand, five hundred fifty-one".