21531265 has 16 divisors (see below), whose sum is σ = 31266432. Its totient is φ = 13895424.

The previous prime is 21531233. The next prime is 21531269. The reversal of 21531265 is 56213512.

It is a cyclic number.

It is not a de Polignac number, because 21531265 - 2⁵ = 21531233 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21531269) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17499 + ... + 18688.

It is an arithmetic number, because the mean of its divisors is an integer number (1954152).

Almost surely, 2^21531265 is an apocalyptic number.

It is an amenable number.

21531265 is a deficient number, since it is larger than the sum of its proper divisors (9735167).

21531265 is a wasteful number, since it uses less digits than its factorization.

21531265 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36216.

The product of its digits is 1800, while the sum is 25.

The square root of 21531265 is about 4640.1794146347. The cubic root of 21531265 is about 278.1996090710.

Adding to 21531265 its reverse (56213512), we get a palindrome (77744777).

The spelling of 21531265 in words is "twenty-one million, five hundred thirty-one thousand, two hundred sixty-five".