21066661 has 16 divisors (see below), whose sum is σ = 26909568. Its totient is φ = 16012800.

The previous prime is 21066641. The next prime is 21066677. The reversal of 21066661 is 16666012.

It is a cyclic number.

It is not a de Polignac number, because 21066661 - 2¹³ = 21058469 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21066601) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 180 + ... + 6493.

It is an arithmetic number, because the mean of its divisors is an integer number (1681848).

Almost surely, 2^21066661 is an apocalyptic number.

It is an amenable number.

21066661 is a deficient number, since it is larger than the sum of its proper divisors (5842907).

21066661 is a wasteful number, since it uses less digits than its factorization.

21066661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6732.

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 21066661 is about 4589.8432435106. The cubic root of 21066661 is about 276.1840341254.

The spelling of 21066661 in words is "twenty-one million, sixty-six thousand, six hundred sixty-one".