21573581 has 4 divisors (see below), whose sum is σ = 21585792. Its totient is φ = 21561372.

The previous prime is 21573547. The next prime is 21573583. The reversal of 21573581 is 18537512.

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 not a de Polignac number, because 21573581 - 2¹⁰ = 21572557 is a prime.

It is a super-2 number, since 2×21573581² = 930838794327122, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21573583) 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, 2891 + ... + 7176.

It is an arithmetic number, because the mean of its divisors is an integer number (5396448).

Almost surely, 2^21573581 is an apocalyptic number.

It is an amenable number.

21573581 is a deficient number, since it is larger than the sum of its proper divisors (12211).

21573581 is a wasteful number, since it uses less digits than its factorization.

21573581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12210.

The product of its digits is 8400, while the sum is 32.

The square root of 21573581 is about 4644.7369139705. The cubic root of 21573581 is about 278.3817409759.

The spelling of 21573581 in words is "twenty-one million, five hundred seventy-three thousand, five hundred eighty-one".