21666544 has 10 divisors (see below), whose sum is σ = 41978960. Its totient is φ = 10833264.

The previous prime is 21666493. The next prime is 21666553. The reversal of 21666544 is 44566612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 677064 + ... + 677095.

It is an arithmetic number, because the mean of its divisors is an integer number (4197896).

Almost surely, 2^21666544 is an apocalyptic number.

It is an amenable number.

21666544 is a deficient number, since it is larger than the sum of its proper divisors (20312416).

21666544 is a wasteful number, since it uses less digits than its factorization.

21666544 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1354167 (or 1354161 counting only the distinct ones).

The product of its digits is 34560, while the sum is 34.

The square root of 21666544 is about 4654.7335047240. The cubic root of 21666544 is about 278.7810274672.

The spelling of 21666544 in words is "twenty-one million, six hundred sixty-six thousand, five hundred forty-four".