21251815211 has 16 divisors (see below), whose sum is σ = 23522565888. Its totient is φ = 19037810400.

The previous prime is 21251815199. The next prime is 21251815219. The reversal of 21251815211 is 11251815212.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21251815211 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21251815219) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1784900 + ... + 1796766.

It is an arithmetic number, because the mean of its divisors is an integer number (1470160368).

Almost surely, 2^21251815211 is an apocalyptic number.

21251815211 is a deficient number, since it is larger than the sum of its proper divisors (2270750677).

21251815211 is a wasteful number, since it uses less digits than its factorization.

21251815211 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14242.

The product of its digits is 1600, while the sum is 29.

Subtracting from 21251815211 its reverse (11251815212), we obtain a palindrome (9999999999).

The spelling of 21251815211 in words is "twenty-one billion, two hundred fifty-one million, eight hundred fifteen thousand, two hundred eleven".