21521265 has 16 divisors (see below), whose sum is σ = 34613568. Its totient is φ = 11418176.

The previous prime is 21521263. The next prime is 21521299. The reversal of 21521265 is 56212512.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21521265 - 2¹ = 21521263 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21521263) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 687 + ... + 6596.

It is an arithmetic number, because the mean of its divisors is an integer number (2163348).

Almost surely, 2^21521265 is an apocalyptic number.

It is an amenable number.

21521265 is a deficient number, since it is larger than the sum of its proper divisors (13092303).

21521265 is a wasteful number, since it uses less digits than its factorization.

21521265 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7488.

The product of its digits is 1200, while the sum is 24.

The square root of 21521265 is about 4639.1017449502. The cubic root of 21521265 is about 278.1565333097.

Adding to 21521265 its reverse (56212512), we get a palindrome (77733777).

The spelling of 21521265 in words is "twenty-one million, five hundred twenty-one thousand, two hundred sixty-five".