21806690 has 16 divisors (see below), whose sum is σ = 40313592. Its totient is φ = 8486784.

The previous prime is 21806663. The next prime is 21806723. The reversal of 21806690 is 9660812.

It can be written as a sum of positive squares in 4 ways, for example, as 15155449 + 6651241 = 3893^2 + 2579^2 .

It is a super-2 number, since 2×21806690² = 951063457512200, which contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 29099 + ... + 29838.

Almost surely, 2^21806690 is an apocalyptic number.

21806690 is a deficient number, since it is larger than the sum of its proper divisors (18506902).

21806690 is a wasteful number, since it uses less digits than its factorization.

21806690 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 58981.

The product of its (nonzero) digits is 5184, while the sum is 32.

The square root of 21806690 is about 4669.7633773030. The cubic root of 21806690 is about 279.3808171427.

The spelling of 21806690 in words is "twenty-one million, eight hundred six thousand, six hundred ninety".