21506304021 has 8 divisors (see below), whose sum is σ = 29145155424. Its totient is φ = 14102494320.

The previous prime is 21506304007. The next prime is 21506304023. The reversal of 21506304021 is 12040360512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21506304021 - 2³⁰ = 20432562197 is a prime.

It is a super-2 number, since 2×21506304021² (a number of 21 digits) contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21506303982 and 21506304000.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21506304023) 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 7 ways as a sum of consecutive naturals, for example, 58760211 + ... + 58760576.

It is an arithmetic number, because the mean of its divisors is an integer number (3643144428).

Almost surely, 2^21506304021 is an apocalyptic number.

It is an amenable number.

21506304021 is a deficient number, since it is larger than the sum of its proper divisors (7638851403).

21506304021 is a wasteful number, since it uses less digits than its factorization.

21506304021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 117520851.

The product of its (nonzero) digits is 1440, while the sum is 24.

Adding to 21506304021 its reverse (12040360512), we get a palindrome (33546664533).

The spelling of 21506304021 in words is "twenty-one billion, five hundred six million, three hundred four thousand, twenty-one".