21424221 has 72 divisors (see below), whose sum is σ = 40209624. Its totient is φ = 10886400.

The previous prime is 21424217. The next prime is 21424223. The reversal of 21424221 is 12242412.

21424221 is a `hidden beast` number, since 21 + 424 + 221 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 9272025 + 12152196 = 3045^2 + 3486^2 .

It is not a de Polignac number, because 21424221 - 2² = 21424217 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21424194 and 21424203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21424223) 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 71 ways as a sum of consecutive naturals, for example, 212071 + ... + 212171.

It is an arithmetic number, because the mean of its divisors is an integer number (558467).

Almost surely, 2^21424221 is an apocalyptic number.

21424221 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21424221 is a deficient number, since it is larger than the sum of its proper divisors (18785403).

21424221 is a wasteful number, since it uses less digits than its factorization.

21424221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171 (or 161 counting only the distinct ones).

The product of its digits is 256, while the sum is 18.

The square root of 21424221 is about 4628.6305750189. The cubic root of 21424221 is about 277.7378141559.

Adding to 21424221 its reverse (12242412), we get a palindrome (33666633).

The spelling of 21424221 in words is "twenty-one million, four hundred twenty-four thousand, two hundred twenty-one".