21431205 has 12 divisors (see below), whose sum is σ = 37147500. Its totient is φ = 11429952.

The previous prime is 21431197. The next prime is 21431209. The reversal of 21431205 is 50213412.

It can be written as a sum of positive squares in 2 ways, for example, as 6937956 + 14493249 = 2634^2 + 3807^2 .

It is not a de Polignac number, because 21431205 - 2³ = 21431197 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21431209) 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 11 ways as a sum of consecutive naturals, for example, 238080 + ... + 238169.

It is an arithmetic number, because the mean of its divisors is an integer number (3095625).

Almost surely, 2^21431205 is an apocalyptic number.

It is an amenable number.

21431205 is a deficient number, since it is larger than the sum of its proper divisors (15716295).

21431205 is a wasteful number, since it uses less digits than its factorization.

21431205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 476260 (or 476257 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 18.

The square root of 21431205 is about 4629.3849483490. The cubic root of 21431205 is about 277.7679904403.

Adding to 21431205 its reverse (50213412), we get a palindrome (71644617).

The spelling of 21431205 in words is "twenty-one million, four hundred thirty-one thousand, two hundred five".