21131265 has 16 divisors (see below), whose sum is σ = 33897600. Its totient is φ = 11240832.

The previous prime is 21131251. The next prime is 21131269. The reversal of 21131265 is 56213112.

It is not a de Polignac number, because 21131265 - 2⁷ = 21131137 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21131269) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4981 + ... + 8189.

It is an arithmetic number, because the mean of its divisors is an integer number (2118600).

Almost surely, 2^21131265 is an apocalyptic number.

It is an amenable number.

21131265 is a deficient number, since it is larger than the sum of its proper divisors (12766335).

21131265 is a wasteful number, since it uses less digits than its factorization.

21131265 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3656.

The product of its digits is 360, while the sum is 21.

The square root of 21131265 is about 4596.8755693405. The cubic root of 21131265 is about 276.4660656154.

Adding to 21131265 its reverse (56213112), we get a palindrome (77344377).

The spelling of 21131265 in words is "twenty-one million, one hundred thirty-one thousand, two hundred sixty-five".