21545521 has 4 divisors (see below), whose sum is σ = 22288500. Its totient is φ = 20802544.

The previous prime is 21545509. The next prime is 21545551. The reversal of 21545521 is 12554512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 15713296 + 5832225 = 3964^2 + 2415^2 .

It is a cyclic number.

It is not a de Polignac number, because 21545521 - 2⁷ = 21545393 is a prime.

It is a super-2 number, since 2×21545521² = 928418950322882, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21545501) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 371446 + ... + 371503.

It is an arithmetic number, because the mean of its divisors is an integer number (5572125).

Almost surely, 2^21545521 is an apocalyptic number.

It is an amenable number.

21545521 is a deficient number, since it is larger than the sum of its proper divisors (742979).

21545521 is an equidigital number, since it uses as much as digits as its factorization.

21545521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 742978.

The product of its digits is 2000, while the sum is 25.

The square root of 21545521 is about 4641.7153079438. The cubic root of 21545521 is about 278.2609948224.

The spelling of 21545521 in words is "twenty-one million, five hundred forty-five thousand, five hundred twenty-one".