21420321 has 32 divisors (see below), whose sum is σ = 32199552. Its totient is φ = 12579840.

The previous prime is 21420293. The next prime is 21420331. The reversal of 21420321 is 12302412.

It is not a de Polignac number, because 21420321 - 2⁶ = 21420257 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21420321.

It is not an unprimeable number, because it can be changed into a prime (21420331) 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 31 ways as a sum of consecutive naturals, for example, 88761 + ... + 89001.

It is an arithmetic number, because the mean of its divisors is an integer number (1006236).

Almost surely, 2^21420321 is an apocalyptic number.

It is an amenable number.

21420321 is a deficient number, since it is larger than the sum of its proper divisors (10779231).

21420321 is a wasteful number, since it uses less digits than its factorization.

21420321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 353.

The product of its (nonzero) digits is 96, while the sum is 15.

The square root of 21420321 is about 4628.2092649317. The cubic root of 21420321 is about 277.7209602844.

Adding to 21420321 its reverse (12302412), we get a palindrome (33722733).

The spelling of 21420321 in words is "twenty-one million, four hundred twenty thousand, three hundred twenty-one".