21275581 has 4 divisors (see below), whose sum is σ = 21298464. Its totient is φ = 21252700.

The previous prime is 21275567. The next prime is 21275587. The reversal of 21275581 is 18557212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21275581 is a prime.

It is a super-2 number, since 2×21275581² = 905300693775122, which contains 22 as substring.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21275587) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9985 + ... + 11926.

It is an arithmetic number, because the mean of its divisors is an integer number (5324616).

Almost surely, 2^21275581 is an apocalyptic number.

It is an amenable number.

21275581 is a deficient number, since it is larger than the sum of its proper divisors (22883).

21275581 is an equidigital number, since it uses as much as digits as its factorization.

21275581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22882.

The product of its digits is 5600, while the sum is 31.

The square root of 21275581 is about 4612.5460431306. The cubic root of 21275581 is about 277.0940133646.

The spelling of 21275581 in words is "twenty-one million, two hundred seventy-five thousand, five hundred eighty-one".