21205424215 has 16 divisors (see below), whose sum is σ = 27204959808. Its totient is φ = 15811416576.

The previous prime is 21205424209. The next prime is 21205424239. The reversal of 21205424215 is 51242450212.

It is a happy number.

It is not a de Polignac number, because 21205424215 - 2⁷ = 21205424087 is a prime.

It is a super-2 number, since 2×21205424215² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1202292 + ... + 1219801.

It is an arithmetic number, because the mean of its divisors is an integer number (1700309988).

Almost surely, 2^21205424215 is an apocalyptic number.

21205424215 is a deficient number, since it is larger than the sum of its proper divisors (5999535593).

21205424215 is a wasteful number, since it uses less digits than its factorization.

21205424215 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2422218.

The product of its (nonzero) digits is 6400, while the sum is 28.

Adding to 21205424215 its reverse (51242450212), we get a palindrome (72447874427).

The spelling of 21205424215 in words is "twenty-one billion, two hundred five million, four hundred twenty-four thousand, two hundred fifteen".