21521212511 has 4 divisors (see below), whose sum is σ = 21780504312. Its totient is φ = 21261920712.

The previous prime is 21521212507. The next prime is 21521212523. The reversal of 21521212511 is 11521212512.

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

It is a cyclic number.

It is not a de Polignac number, because 21521212511 - 2² = 21521212507 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 (21521212501) 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, 129645776 + ... + 129645941.

It is an arithmetic number, because the mean of its divisors is an integer number (5445126078).

Almost surely, 2^21521212511 is an apocalyptic number.

21521212511 is a deficient number, since it is larger than the sum of its proper divisors (259291801).

21521212511 is an equidigital number, since it uses as much as digits as its factorization.

21521212511 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 259291800.

The product of its digits is 400, while the sum is 23.

Subtracting from 21521212511 its reverse (11521212512), we obtain a palindrome (9999999999).

The spelling of 21521212511 in words is "twenty-one billion, five hundred twenty-one million, two hundred twelve thousand, five hundred eleven".