21999681 has 20 divisors (see below), whose sum is σ = 35852784. Its totient is φ = 13332600.

The previous prime is 21999673. The next prime is 21999689. The reversal of 21999681 is 18699912.

It is an interprime number because it is at equal distance from previous prime (21999673) and next prime (21999689).

It is not a de Polignac number, because 21999681 - 2³ = 21999673 is a prime.

It is a super-2 number, since 2×21999681² = 967971928203522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21999689) 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 19 ways as a sum of consecutive naturals, for example, 11455 + ... + 13236.

Almost surely, 2^21999681 is an apocalyptic number.

It is an amenable number.

21999681 is a deficient number, since it is larger than the sum of its proper divisors (13853103).

21999681 is a wasteful number, since it uses less digits than its factorization.

21999681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24714 (or 24705 counting only the distinct ones).

The product of its digits is 69984, while the sum is 45.

The square root of 21999681 is about 4690.3817541859. The cubic root of 21999681 is about 280.2025787400.

The spelling of 21999681 in words is "twenty-one million, nine hundred ninety-nine thousand, six hundred eighty-one".