21786681 has 32 divisors (see below), whose sum is σ = 35481600. Its totient is φ = 11620224.

The previous prime is 21786679. The next prime is 21786683. The reversal of 21786681 is 18668712.

It is an interprime number because it is at equal distance from previous prime (21786679) and next prime (21786683).

It is not a de Polignac number, because 21786681 - 2¹ = 21786679 is a prime.

It is a super-2 number, since 2×21786681² = 949318937991522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21786683) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 20245 + ... + 21293.

It is an arithmetic number, because the mean of its divisors is an integer number (1108800).

Almost surely, 2^21786681 is an apocalyptic number.

21786681 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21786681 is a deficient number, since it is larger than the sum of its proper divisors (13694919).

21786681 is a wasteful number, since it uses less digits than its factorization.

21786681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1125.

The product of its digits is 32256, while the sum is 39.

The square root of 21786681 is about 4667.6204858579. The cubic root of 21786681 is about 279.2953412114.

The spelling of 21786681 in words is "twenty-one million, seven hundred eighty-six thousand, six hundred eighty-one".