21666447 has 20 divisors (see below), whose sum is σ = 35309736. Its totient is φ = 13130640.

The previous prime is 21666443. The next prime is 21666481. The reversal of 21666447 is 74466612.

It is not a de Polignac number, because 21666447 - 2² = 21666443 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21666443) by changing a digit.

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 19 ways as a sum of consecutive naturals, for example, 11268 + ... + 13049.

Almost surely, 2^21666447 is an apocalyptic number.

21666447 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21666447 is a deficient number, since it is larger than the sum of its proper divisors (13643289).

21666447 is a wasteful number, since it uses less digits than its factorization.

21666447 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24340 (or 24331 counting only the distinct ones).

The product of its digits is 48384, while the sum is 36.

The square root of 21666447 is about 4654.7230852114. The cubic root of 21666447 is about 278.7806114371.

The spelling of 21666447 in words is "twenty-one million, six hundred sixty-six thousand, four hundred forty-seven".