21166621 has 8 divisors (see below), whose sum is σ = 24753344. Its totient is φ = 17720640.

The previous prime is 21166609. The next prime is 21166643. The reversal of 21166621 is 12666112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21166621 - 2¹⁷ = 21035549 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21166721) 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 7 ways as a sum of consecutive naturals, for example, 34860 + ... + 35461.

It is an arithmetic number, because the mean of its divisors is an integer number (3094168).

Almost surely, 2^21166621 is an apocalyptic number.

It is an amenable number.

21166621 is a deficient number, since it is larger than the sum of its proper divisors (3586723).

21166621 is an equidigital number, since it uses as much as digits as its factorization.

21166621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 70371.

The product of its digits is 864, while the sum is 25.

The square root of 21166621 is about 4600.7196176251. The cubic root of 21166621 is about 276.6201704093.

The spelling of 21166621 in words is "twenty-one million, one hundred sixty-six thousand, six hundred twenty-one".