21666489 has 16 divisors (see below), whose sum is σ = 32116224. Its totient is φ = 12902400.

The previous prime is 21666487. The next prime is 21666493. The reversal of 21666489 is 98466612.

It is not a de Polignac number, because 21666489 - 2¹ = 21666487 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21666489.

It is not an unprimeable number, because it can be changed into a prime (21666481) 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 15 ways as a sum of consecutive naturals, for example, 7752 + ... + 10169.

It is an arithmetic number, because the mean of its divisors is an integer number (2007264).

Almost surely, 2^21666489 is an apocalyptic number.

It is an amenable number.

21666489 is a deficient number, since it is larger than the sum of its proper divisors (10449735).

21666489 is a wasteful number, since it uses less digits than its factorization.

21666489 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17968.

The product of its digits is 124416, while the sum is 42.

The square root of 21666489 is about 4654.7275967558. The cubic root of 21666489 is about 278.7807915740.

It can be divided in two parts, 21666 and 489, that added together give a triangular number (22155 = T₂₁₀).

The spelling of 21666489 in words is "twenty-one million, six hundred sixty-six thousand, four hundred eighty-nine".