21806131 has 4 divisors (see below), whose sum is σ = 21932352. Its totient is φ = 21679912.

The previous prime is 21806123. The next prime is 21806143. The reversal of 21806131 is 13160812.

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 21806131 - 2³ = 21806123 is a prime.

It is a super-2 number, since 2×21806131² = 951014698378322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21806111) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 62851 + ... + 63196.

It is an arithmetic number, because the mean of its divisors is an integer number (5483088).

Almost surely, 2^21806131 is an apocalyptic number.

21806131 is a deficient number, since it is larger than the sum of its proper divisors (126221).

21806131 is a wasteful number, since it uses less digits than its factorization.

21806131 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 126220.

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 21806131 is about 4669.7035237796. The cubic root of 21806131 is about 279.3784298751.

Adding to 21806131 its reverse (13160812), we get a palindrome (34966943).

The spelling of 21806131 in words is "twenty-one million, eight hundred six thousand, one hundred thirty-one".