21206307 has 16 divisors (see below), whose sum is σ = 29520288. Its totient is φ = 13528320.

The previous prime is 21206303. The next prime is 21206323. The reversal of 21206307 is 70360212.

It is a happy number.

It is not a de Polignac number, because 21206307 - 2² = 21206303 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21206303) 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 15 ways as a sum of consecutive naturals, for example, 4893 + ... + 8145.

It is an arithmetic number, because the mean of its divisors is an integer number (1845018).

Almost surely, 2^21206307 is an apocalyptic number.

21206307 is a deficient number, since it is larger than the sum of its proper divisors (8313981).

21206307 is a wasteful number, since it uses less digits than its factorization.

21206307 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3350.

The product of its (nonzero) digits is 504, while the sum is 21.

The square root of 21206307 is about 4605.0306187907. The cubic root of 21206307 is about 276.7929439198.

Adding to 21206307 its sum of digits (21), we get a triangular number (21206328 = T₆₅₁₂).

Adding to 21206307 its reverse (70360212), we get a palindrome (91566519).

The spelling of 21206307 in words is "twenty-one million, two hundred six thousand, three hundred seven".