21007221 has 8 divisors (see below), whose sum is σ = 28106400. Its totient is φ = 13956432.

The previous prime is 21007213. The next prime is 21007229. The reversal of 21007221 is 12270012.

It is an interprime number because it is at equal distance from previous prime (21007213) and next prime (21007229).

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

It is not a de Polignac number, because 21007221 - 2³ = 21007213 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21007221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21007229) 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 7 ways as a sum of consecutive naturals, for example, 11071 + ... + 12828.

It is an arithmetic number, because the mean of its divisors is an integer number (3513300).

Almost surely, 2^21007221 is an apocalyptic number.

It is an amenable number.

21007221 is a deficient number, since it is larger than the sum of its proper divisors (7099179).

21007221 is a wasteful number, since it uses less digits than its factorization.

21007221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24195.

The product of its (nonzero) digits is 56, while the sum is 15.

The square root of 21007221 is about 4583.3635029310. The cubic root of 21007221 is about 275.9240365404.

Adding to 21007221 its reverse (12270012), we get a palindrome (33277233).

The spelling of 21007221 in words is "twenty-one million, seven thousand, two hundred twenty-one".