21401221 has 4 divisors (see below), whose sum is σ = 21923244. Its totient is φ = 20879200.

The previous prime is 21401203. The next prime is 21401251. The reversal of 21401221 is 12210412.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 470596 + 20930625 = 686^2 + 4575^2 .

It is a cyclic number.

It is not a de Polignac number, because 21401221 - 2¹⁵ = 21368453 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21401251) 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 3 ways as a sum of consecutive naturals, for example, 260950 + ... + 261031.

It is an arithmetic number, because the mean of its divisors is an integer number (5480811).

Almost surely, 2^21401221 is an apocalyptic number.

It is an amenable number.

21401221 is a deficient number, since it is larger than the sum of its proper divisors (522023).

21401221 is an equidigital number, since it uses as much as digits as its factorization.

21401221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 522022.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21401221 is about 4626.1453716890. The cubic root of 21401221 is about 277.6383899726.

Adding to 21401221 its reverse (12210412), we get a palindrome (33611633).

The spelling of 21401221 in words is "twenty-one million, four hundred one thousand, two hundred twenty-one".