21521375 has 8 divisors (see below), whose sum is σ = 26858832. Its totient is φ = 17217000.

The previous prime is 21521369. The next prime is 21521387. The reversal of 21521375 is 57312512.

It is a de Polignac number, because none of the positive numbers 2^k-21521375 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 85961 + ... + 86210.

It is an arithmetic number, because the mean of its divisors is an integer number (3357354).

Almost surely, 2^21521375 is an apocalyptic number.

21521375 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21521375 is a deficient number, since it is larger than the sum of its proper divisors (5337457).

21521375 is an equidigital number, since it uses as much as digits as its factorization.

21521375 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 172186 (or 172176 counting only the distinct ones).

The product of its digits is 2100, while the sum is 26.

The square root of 21521375 is about 4639.1136006785. The cubic root of 21521375 is about 278.1570072157.

Adding to 21521375 its reverse (57312512), we get a palindrome (78833887).

The spelling of 21521375 in words is "twenty-one million, five hundred twenty-one thousand, three hundred seventy-five".