21236221 has 4 divisors (see below), whose sum is σ = 21363552. Its totient is φ = 21108892.

The previous prime is 21236219. The next prime is 21236239. The reversal of 21236221 is 12263212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21236221 - 2¹ = 21236219 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21236251) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 63415 + ... + 63748.

It is an arithmetic number, because the mean of its divisors is an integer number (5340888).

Almost surely, 2^21236221 is an apocalyptic number.

It is an amenable number.

21236221 is a deficient number, since it is larger than the sum of its proper divisors (127331).

21236221 is a wasteful number, since it uses less digits than its factorization.

21236221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 127330.

The product of its digits is 288, while the sum is 19.

The square root of 21236221 is about 4608.2774439046. The cubic root of 21236221 is about 276.9230324806.

Adding to 21236221 its reverse (12263212), we get a palindrome (33499433).

The spelling of 21236221 in words is "twenty-one million, two hundred thirty-six thousand, two hundred twenty-one".