21285681 has 32 divisors (see below), whose sum is σ = 31488000. Its totient is φ = 12737088.

The previous prime is 21285679. The next prime is 21285703. The reversal of 21285681 is 18658212.

It is not a de Polignac number, because 21285681 - 2¹ = 21285679 is a prime.

It is a super-2 number, since 2×21285681² = 906160431267522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21285611) 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, 130506 + ... + 130668.

It is an arithmetic number, because the mean of its divisors is an integer number (984000).

Almost surely, 2^21285681 is an apocalyptic number.

It is an amenable number.

21285681 is a deficient number, since it is larger than the sum of its proper divisors (10202319).

21285681 is a wasteful number, since it uses less digits than its factorization.

21285681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 293.

The product of its digits is 7680, while the sum is 33.

The square root of 21285681 is about 4613.6407532447. The cubic root of 21285681 is about 277.1378540286.

The spelling of 21285681 in words is "twenty-one million, two hundred eighty-five thousand, six hundred eighty-one".