21689081 has 2 divisors, whose sum is σ = 21689082. Its totient is φ = 21689080.

The previous prime is 21689077. The next prime is 21689111. The reversal of 21689081 is 18098612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13623481 + 8065600 = 3691^2 + 2840^2 .

It is a cyclic number.

It is not a de Polignac number, because 21689081 - 2² = 21689077 is a prime.

It is a super-2 number, since 2×21689081² = 940832469249122, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21689021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10844540 + 10844541.

It is an arithmetic number, because the mean of its divisors is an integer number (10844541).

Almost surely, 2^21689081 is an apocalyptic number.

It is an amenable number.

21689081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21689081 is an equidigital number, since it uses as much as digits as its factorization.

21689081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6912, while the sum is 35.

The square root of 21689081 is about 4657.1537445096. The cubic root of 21689081 is about 278.8776543348.

The spelling of 21689081 in words is "twenty-one million, six hundred eighty-nine thousand, eighty-one".