21691805 has 12 divisors (see below), whose sum is σ = 26761140. Its totient is φ = 16879104.

The previous prime is 21691793. The next prime is 21691843. The reversal of 21691805 is 50819612.

It can be written as a sum of positive squares in 6 ways, for example, as 6160324 + 15531481 = 2482^2 + 3941^2 .

It is not a de Polignac number, because 21691805 - 2¹² = 21687709 is a prime.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5261 + ... + 8429.

It is an arithmetic number, because the mean of its divisors is an integer number (2230095).

Almost surely, 2^21691805 is an apocalyptic number.

It is an amenable number.

21691805 is a deficient number, since it is larger than the sum of its proper divisors (5069335).

21691805 is an equidigital number, since it uses as much as digits as its factorization.

21691805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3248 (or 3211 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 32.

The square root of 21691805 is about 4657.4461886317. The cubic root of 21691805 is about 278.8893288871.

The spelling of 21691805 in words is "twenty-one million, six hundred ninety-one thousand, eight hundred five".