21561375 has 32 divisors (see below), whose sum is σ = 39147264. Its totient is φ = 10452000.

The previous prime is 21561359. The next prime is 21561377. The reversal of 21561375 is 57316512.

It is not a de Polignac number, because 21561375 - 2⁴ = 21561359 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561377) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 1512 + ... + 6738.

It is an arithmetic number, because the mean of its divisors is an integer number (1223352).

Almost surely, 2^21561375 is an apocalyptic number.

21561375 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21561375 is a deficient number, since it is larger than the sum of its proper divisors (17585889).

21561375 is a wasteful number, since it uses less digits than its factorization.

21561375 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5256 (or 5246 counting only the distinct ones).

The product of its digits is 6300, while the sum is 30.

The square root of 21561375 is about 4643.4227677436. The cubic root of 21561375 is about 278.3292297035.

Adding to 21561375 its reverse (57316512), we get a palindrome (78877887).

The spelling of 21561375 in words is "twenty-one million, five hundred sixty-one thousand, three hundred seventy-five".