21986581 has 4 divisors (see below), whose sum is σ = 22121632. Its totient is φ = 21851532.

The previous prime is 21986567. The next prime is 21986599. The reversal of 21986581 is 18568912.

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 21986581 - 2¹¹ = 21984533 is a prime.

It is a super-2 number, since 2×21986581² = 966819488139122, 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 (21986521) 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, 67281 + ... + 67606.

It is an arithmetic number, because the mean of its divisors is an integer number (5530408).

Almost surely, 2^21986581 is an apocalyptic number.

It is an amenable number.

21986581 is a deficient number, since it is larger than the sum of its proper divisors (135051).

21986581 is a wasteful number, since it uses less digits than its factorization.

21986581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 135050.

The product of its digits is 34560, while the sum is 40.

The square root of 21986581 is about 4688.9850714200. The cubic root of 21986581 is about 280.1469509243.

The spelling of 21986581 in words is "twenty-one million, nine hundred eighty-six thousand, five hundred eighty-one".