21561055 has 8 divisors (see below), whose sum is σ = 25905744. Its totient is φ = 17227200.

The previous prime is 21561041. The next prime is 21561077. The reversal of 21561055 is 55016512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21561055 - 2¹⁹ = 21036767 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2635 + ... + 7075.

It is an arithmetic number, because the mean of its divisors is an integer number (3238218).

Almost surely, 2^21561055 is an apocalyptic number.

21561055 is a deficient number, since it is larger than the sum of its proper divisors (4344689).

21561055 is an equidigital number, since it uses as much as digits as its factorization.

21561055 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5417.

The product of its (nonzero) digits is 1500, while the sum is 25.

The square root of 21561055 is about 4643.3883102752. The cubic root of 21561055 is about 278.3278527692.

Adding to 21561055 its reverse (55016512), we get a palindrome (76577567).

The spelling of 21561055 in words is "twenty-one million, five hundred sixty-one thousand, fifty-five".