21351321 has 6 divisors (see below), whose sum is σ = 30840810. Its totient is φ = 14234208.

The previous prime is 21351311. The next prime is 21351347. The reversal of 21351321 is 12315312.

It can be written as a sum of positive squares in only one way, i.e., 21261321 + 90000 = 4611^2 + 300^2 .

It is not a de Polignac number, because 21351321 - 2⁵ = 21351289 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21351294 and 21351303.

It is not an unprimeable number, because it can be changed into a prime (21351311) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1186176 + ... + 1186193.

It is an arithmetic number, because the mean of its divisors is an integer number (5140135).

Almost surely, 2^21351321 is an apocalyptic number.

It is an amenable number.

21351321 is a deficient number, since it is larger than the sum of its proper divisors (9489489).

21351321 is a wasteful number, since it uses less digits than its factorization.

21351321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2372375 (or 2372372 counting only the distinct ones).

The product of its digits is 180, while the sum is 18.

The square root of 21351321 is about 4620.7489652653. The cubic root of 21351321 is about 277.4224375389.

Adding to 21351321 its reverse (12315312), we get a palindrome (33666633).

The spelling of 21351321 in words is "twenty-one million, three hundred fifty-one thousand, three hundred twenty-one".