21066921 has 6 divisors (see below), whose sum is σ = 30430010. Its totient is φ = 14044608.

The previous prime is 21066863. The next prime is 21066931. The reversal of 21066921 is 12966012.

It can be written as a sum of positive squares in only one way, i.e., 19900521 + 1166400 = 4461^2 + 1080^2 .

It is not a de Polignac number, because 21066921 - 2¹⁰ = 21065897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21066931) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1170376 + ... + 1170393.

Almost surely, 2^21066921 is an apocalyptic number.

It is an amenable number.

21066921 is a deficient number, since it is larger than the sum of its proper divisors (9363089).

21066921 is a wasteful number, since it uses less digits than its factorization.

21066921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2340775 (or 2340772 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21066921 is about 4589.8715668306. The cubic root of 21066921 is about 276.1851703211.

The spelling of 21066921 in words is "twenty-one million, sixty-six thousand, nine hundred twenty-one".