21543553021 has 4 divisors (see below), whose sum is σ = 21543883200. Its totient is φ = 21543222844.

The previous prime is 21543552983. The next prime is 21543553051. The reversal of 21543553021 is 12035534512.

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 not a de Polignac number, because 21543553021 - 2²¹ = 21541455869 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 (21543553051) 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, 30811 + ... + 209848.

It is an arithmetic number, because the mean of its divisors is an integer number (5385970800).

Almost surely, 2^21543553021 is an apocalyptic number.

It is an amenable number.

21543553021 is a deficient number, since it is larger than the sum of its proper divisors (330179).

21543553021 is an equidigital number, since it uses as much as digits as its factorization.

21543553021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 330178.

The product of its (nonzero) digits is 18000, while the sum is 31.

It can be divided in two parts, 21543 and 553021, that added together give a square (574564 = 758²).

The spelling of 21543553021 in words is "twenty-one billion, five hundred forty-three million, five hundred fifty-three thousand, twenty-one".