21809131 has 8 divisors (see below), whose sum is σ = 23749200. Its totient is φ = 19948320.

The previous prime is 21809119. The next prime is 21809143. The reversal of 21809131 is 13190812.

It is an interprime number because it is at equal distance from previous prime (21809119) and next prime (21809143).

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21809131 - 2⁷ = 21809003 is a prime.

It is a super-2 number, since 2×21809131² = 951276389950322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21809096 and 21809105.

It is not an unprimeable number, because it can be changed into a prime (21809101) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 19240 + ... + 20341.

It is an arithmetic number, because the mean of its divisors is an integer number (2968650).

Almost surely, 2^21809131 is an apocalyptic number.

21809131 is a deficient number, since it is larger than the sum of its proper divisors (1940069).

21809131 is a wasteful number, since it uses less digits than its factorization.

21809131 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 39629.

The product of its (nonzero) digits is 432, while the sum is 25.

The square root of 21809131 is about 4670.0247322686. The cubic root of 21809131 is about 279.3912412087.

Adding to 21809131 its reverse (13190812), we get a palindrome (34999943).

It can be divided in two parts, 2180 and 9131, that added together give a palindrome (11311).

The spelling of 21809131 in words is "twenty-one million, eight hundred nine thousand, one hundred thirty-one".