21552321 has 16 divisors (see below), whose sum is σ = 32958464. Its totient is φ = 12271824.

The previous prime is 21552319. The next prime is 21552341. The reversal of 21552321 is 12325512.

It is not a de Polignac number, because 21552321 - 2¹ = 21552319 is a prime.

It is a super-3 number, since 3×21552321³ (a number of 23 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is not an unprimeable number, because it can be changed into a prime (21552341) 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 15 ways as a sum of consecutive naturals, for example, 4776 + ... + 8118.

It is an arithmetic number, because the mean of its divisors is an integer number (2059904).

Almost surely, 2^21552321 is an apocalyptic number.

21552321 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21552321 is a deficient number, since it is larger than the sum of its proper divisors (11406143).

21552321 is a wasteful number, since it uses less digits than its factorization.

21552321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3660.

The product of its digits is 600, while the sum is 21.

The square root of 21552321 is about 4642.4477379934. The cubic root of 21552321 is about 278.2902658054.

Multiplying 21552321 by its sum of digits (21), we get a triangular number (452598741 = T₃₀₀₈₆).

Adding to 21552321 its reverse (12325512), we get a palindrome (33877833).

The spelling of 21552321 in words is "twenty-one million, five hundred fifty-two thousand, three hundred twenty-one".