21206403 has 6 divisors (see below), whose sum is σ = 30631484. Its totient is φ = 14137596.

The previous prime is 21206401. The next prime is 21206407. The reversal of 21206403 is 30460212.

It is a happy number.

21206403 is a `hidden beast` number, since 2 + 1 + 20 + 640 + 3 = 666.

It is not a de Polignac number, because 21206403 - 2¹ = 21206401 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21206401) 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 5 ways as a sum of consecutive naturals, for example, 1178125 + ... + 1178142.

Almost surely, 2^21206403 is an apocalyptic number.

21206403 is a deficient number, since it is larger than the sum of its proper divisors (9425081).

21206403 is a wasteful number, since it uses less digits than its factorization.

21206403 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2356273 (or 2356270 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 18.

The square root of 21206403 is about 4605.0410421624. The cubic root of 21206403 is about 276.7933615956.

Adding to 21206403 its reverse (30460212), we get a palindrome (51666615).

It can be divided in two parts, 21206 and 403, that added together give a square (21609 = 147²).

The spelling of 21206403 in words is "twenty-one million, two hundred six thousand, four hundred three".