21405666 has 32 divisors (see below), whose sum is σ = 45527040. Its totient is φ = 6690384.

The previous prime is 21405661. The next prime is 21405667. The reversal of 21405666 is 66650412.

It is not an unprimeable number, because it can be changed into a prime (21405661) 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, 10831 + ... + 12653.

It is an arithmetic number, because the mean of its divisors is an integer number (1422720).

Almost surely, 2^21405666 is an apocalyptic number.

21405666 is an abundant number, since it is smaller than the sum of its proper divisors (24121374).

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

21405666 is a wasteful number, since it uses less digits than its factorization.

21405666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1950.

The product of its (nonzero) digits is 8640, while the sum is 30.

The square root of 21405666 is about 4626.6257683111. The cubic root of 21405666 is about 277.6576103279.

The spelling of 21405666 in words is "twenty-one million, four hundred five thousand, six hundred sixty-six".