21215220642521 has 4 divisors (see below), whose sum is σ = 21250171583232. Its totient is φ = 21180269701812.

The previous prime is 21215220642439. The next prime is 21215220642547. The reversal of 21215220642521 is 12524602251212.

It is a happy number.

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 a de Polignac number, because none of the positive numbers 2^k-21215220642521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215220642221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17475469445 + ... + 17475470658.

It is an arithmetic number, because the mean of its divisors is an integer number (5312542895808).

Almost surely, 2^{21215220642521} is an apocalyptic number.

It is an amenable number.

21215220642521 is a deficient number, since it is larger than the sum of its proper divisors (34950940711).

21215220642521 is an equidigital number, since it uses as much as digits as its factorization.

21215220642521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34950940710.

The product of its (nonzero) digits is 38400, while the sum is 35.

Adding to 21215220642521 its reverse (12524602251212), we get a palindrome (33739822893733).

The spelling of 21215220642521 in words is "twenty-one trillion, two hundred fifteen billion, two hundred twenty million, six hundred forty-two thousand, five hundred twenty-one".