21887581 has 4 divisors (see below), whose sum is σ = 22593664. Its totient is φ = 21181500.

The previous prime is 21887557. The next prime is 21887587. The reversal of 21887581 is 18578812.

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 21887581 - 2⁵ = 21887549 is a prime.

It is a super-2 number, since 2×21887581² = 958132404063122, 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 (21887587) 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, 352995 + ... + 353056.

It is an arithmetic number, because the mean of its divisors is an integer number (5648416).

Almost surely, 2^21887581 is an apocalyptic number.

It is an amenable number.

21887581 is a deficient number, since it is larger than the sum of its proper divisors (706083).

21887581 is an equidigital number, since it uses as much as digits as its factorization.

21887581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 706082.

The product of its digits is 35840, while the sum is 40.

The square root of 21887581 is about 4678.4165056138. The cubic root of 21887581 is about 279.7258413423.

The spelling of 21887581 in words is "twenty-one million, eight hundred eighty-seven thousand, five hundred eighty-one".