21166531 has 4 divisors (see below), whose sum is σ = 21211200. Its totient is φ = 21121864.

The previous prime is 21166529. The next prime is 21166559. The reversal of 21166531 is 13566112.

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 21166531 - 2¹ = 21166529 is a prime.

It is a super-2 number, since 2×21166531² = 896044069147922, 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 = 21166496 and 21166505.

It is not an unprimeable number, because it can be changed into a prime (21166511) 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, 21616 + ... + 22573.

It is an arithmetic number, because the mean of its divisors is an integer number (5302800).

Almost surely, 2^21166531 is an apocalyptic number.

21166531 is the 2058-th centered decagonal number.

21166531 is a deficient number, since it is larger than the sum of its proper divisors (44669).

21166531 is an equidigital number, since it uses as much as digits as its factorization.

21166531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44668.

The product of its digits is 1080, while the sum is 25.

The square root of 21166531 is about 4600.7098365361. The cubic root of 21166531 is about 276.6197783478.

The spelling of 21166531 in words is "twenty-one million, one hundred sixty-six thousand, five hundred thirty-one".