21120829921 has 4 divisors (see below), whose sum is σ = 21157949700. Its totient is φ = 21083710144.

The previous prime is 21120829909. The next prime is 21120829927. The reversal of 21120829921 is 12992802112.

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 3667513600 + 17453316321 = 60560^2 + 132111^2 .

It is a cyclic number.

It is not a de Polignac number, because 21120829921 - 2¹⁵ = 21120797153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21120829927) 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, 18559036 + ... + 18560173.

It is an arithmetic number, because the mean of its divisors is an integer number (5289487425).

Almost surely, 2^21120829921 is an apocalyptic number.

It is an amenable number.

21120829921 is a deficient number, since it is larger than the sum of its proper divisors (37119779).

21120829921 is an equidigital number, since it uses as much as digits as its factorization.

21120829921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 37119778.

The product of its (nonzero) digits is 10368, while the sum is 37.

It can be divided in two parts, 21120829 and 921, that added together give a triangular number (21121750 = T₆₄₉₉).

The spelling of 21120829921 in words is "twenty-one billion, one hundred twenty million, eight hundred twenty-nine thousand, nine hundred twenty-one".