21306257 has 16 divisors (see below), whose sum is σ = 25850880. Its totient is φ = 17164752.

The previous prime is 21306247. The next prime is 21306281. The reversal of 21306257 is 75260312.

It is not a de Polignac number, because 21306257 - 2⁶ = 21306193 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21306217) 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, 8378 + ... + 10620.

It is an arithmetic number, because the mean of its divisors is an integer number (1615680).

Almost surely, 2^21306257 is an apocalyptic number.

It is an amenable number.

21306257 is a deficient number, since it is larger than the sum of its proper divisors (4544623).

21306257 is a wasteful number, since it uses less digits than its factorization.

21306257 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2332.

The product of its (nonzero) digits is 2520, while the sum is 26.

The square root of 21306257 is about 4615.8701238228. The cubic root of 21306257 is about 277.2271245582.

Adding to 21306257 its reverse (75260312), we get a palindrome (96566569).

The spelling of 21306257 in words is "twenty-one million, three hundred six thousand, two hundred fifty-seven".