21661866 has 12 divisors (see below), whose sum is σ = 46934082. Its totient is φ = 7220616.

The previous prime is 21661853. The next prime is 21661873. The reversal of 21661866 is 66816612.

It can be written as a sum of positive squares in only one way, i.e., 15800625 + 5861241 = 3975^2 + 2421^2 .

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21661866.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 601701 + ... + 601736.

Almost surely, 2^21661866 is an apocalyptic number.

21661866 is an abundant number, since it is smaller than the sum of its proper divisors (25272216).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21661866 is a wasteful number, since it uses less digits than its factorization.

21661866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1203445 (or 1203442 counting only the distinct ones).

The product of its digits is 20736, while the sum is 36.

The square root of 21661866 is about 4654.2309783680. The cubic root of 21661866 is about 278.7609622533.

The spelling of 21661866 in words is "twenty-one million, six hundred sixty-one thousand, eight hundred sixty-six".