21865131 has 6 divisors (see below), whose sum is σ = 31582980. Its totient is φ = 14576748.

The previous prime is 21865121. The next prime is 21865133. The reversal of 21865131 is 13156812.

21865131 is a `hidden beast` number, since 2 + 1 + 8 + 651 + 3 + 1 = 666.

It is not a de Polignac number, because 21865131 - 2⁵ = 21865099 is a prime.

It is a super-2 number, since 2×21865131² = 956167907294322, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21865095 and 21865104.

It is not an unprimeable number, because it can be changed into a prime (21865133) 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 5 ways as a sum of consecutive naturals, for example, 1214721 + ... + 1214738.

It is an arithmetic number, because the mean of its divisors is an integer number (5263830).

Almost surely, 2^21865131 is an apocalyptic number.

21865131 is a deficient number, since it is larger than the sum of its proper divisors (9717849).

21865131 is a wasteful number, since it uses less digits than its factorization.

21865131 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2429465 (or 2429462 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 21865131 is about 4676.0165739655. The cubic root of 21865131 is about 279.6301707513.

The spelling of 21865131 in words is "twenty-one million, eight hundred sixty-five thousand, one hundred thirty-one".