21511221 has 8 divisors (see below), whose sum is σ = 29109984. Its totient is φ = 14126640.

The previous prime is 21511219. The next prime is 21511229. The reversal of 21511221 is 12211512.

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

It is not a de Polignac number, because 21511221 - 2¹ = 21511219 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21511221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21511229) 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, 53310 + ... + 53711.

It is an arithmetic number, because the mean of its divisors is an integer number (3638748).

Almost surely, 2^21511221 is an apocalyptic number.

It is an amenable number.

21511221 is a deficient number, since it is larger than the sum of its proper divisors (7598763).

21511221 is a wasteful number, since it uses less digits than its factorization.

21511221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107091.

The product of its digits is 40, while the sum is 15.

The square root of 21511221 is about 4638.0190814614. The cubic root of 21511221 is about 278.1132545812.

Adding to 21511221 its reverse (12211512), we get a palindrome (33722733).

The spelling of 21511221 in words is "twenty-one million, five hundred eleven thousand, two hundred twenty-one".