21231221 has 8 divisors (see below), whose sum is σ = 23216544. Its totient is φ = 19255120.

The previous prime is 21231173. The next prime is 21231241. The reversal of 21231221 is 12213212.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 21231221 - 2²² = 17036917 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21231196 and 21231205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21231241) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 3071 + ... + 7203.

It is an arithmetic number, because the mean of its divisors is an integer number (2902068).

Almost surely, 2^21231221 is an apocalyptic number.

It is an amenable number.

21231221 is a deficient number, since it is larger than the sum of its proper divisors (1985323).

21231221 is a wasteful number, since it uses less digits than its factorization.

21231221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4611.

The product of its digits is 48, while the sum is 14.

The square root of 21231221 is about 4607.7349099096. The cubic root of 21231221 is about 276.9012972286.

Adding to 21231221 its reverse (12213212), we get a palindrome (33444433).

Subtracting from 21231221 its reverse (12213212), we obtain a square (9018009 = 3003²).

The spelling of 21231221 in words is "twenty-one million, two hundred thirty-one thousand, two hundred twenty-one".