21215525 has 12 divisors (see below), whose sum is σ = 26449572. Its totient is φ = 16880640.

The previous prime is 21215503. The next prime is 21215539. The reversal of 21215525 is 52551212.

It can be written as a sum of positive squares in 6 ways, for example, as 1705636 + 19509889 = 1306^2 + 4417^2 .

It is not a de Polignac number, because 21215525 - 2¹⁴ = 21199141 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21215525.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2627 + ... + 7023.

It is an arithmetic number, because the mean of its divisors is an integer number (2204131).

Almost surely, 2^21215525 is an apocalyptic number.

21215525 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

It is an amenable number.

21215525 is a deficient number, since it is larger than the sum of its proper divisors (5234047).

21215525 is a wasteful number, since it uses less digits than its factorization.

21215525 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4600 (or 4595 counting only the distinct ones).

The product of its digits is 1000, while the sum is 23.

The square root of 21215525 is about 4606.0313720165. The cubic root of 21215525 is about 276.8330437472.

Adding to 21215525 its reverse (52551212), we get a palindrome (73766737).

The spelling of 21215525 in words is "twenty-one million, two hundred fifteen thousand, five hundred twenty-five".