21621321 has 6 divisors (see below), whose sum is σ = 31230810. Its totient is φ = 14414208.

The previous prime is 21621293. The next prime is 21621329. The reversal of 21621321 is 12312612.

21621321 is a `hidden beast` number, since 21 + 621 + 3 + 21 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21261321 + 360000 = 4611^2 + 600^2 .

It is not a de Polignac number, because 21621321 - 2⁵ = 21621289 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21621294 and 21621303.

It is not an unprimeable number, because it can be changed into a prime (21621329) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1201176 + ... + 1201193.

It is an arithmetic number, because the mean of its divisors is an integer number (5205135).

Almost surely, 2^21621321 is an apocalyptic number.

It is an amenable number.

21621321 is a deficient number, since it is larger than the sum of its proper divisors (9609489).

21621321 is a wasteful number, since it uses less digits than its factorization.

21621321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2402375 (or 2402372 counting only the distinct ones).

The product of its digits is 144, while the sum is 18.

The square root of 21621321 is about 4649.8732240783. The cubic root of 21621321 is about 278.5869325831.

Adding to 21621321 its reverse (12312612), we get a palindrome (33933933).

The spelling of 21621321 in words is "twenty-one million, six hundred twenty-one thousand, three hundred twenty-one".