21218457 has 12 divisors (see below), whose sum is σ = 30635664. Its totient is φ = 13057200.

The previous prime is 21218441. The next prime is 21218467. The reversal of 21218457 is 75481212.

It is not a de Polignac number, because 21218457 - 2⁴ = 21218441 is a prime.

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its prime factors.

It is not an unprimeable number, because it can be changed into a prime (21218467) 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, 20419 + ... + 21432.

It is an arithmetic number, because the mean of its divisors is an integer number (2552972).

Almost surely, 2^21218457 is an apocalyptic number.

It is an amenable number.

21218457 is a deficient number, since it is larger than the sum of its proper divisors (9417207).

21218457 is a wasteful number, since it uses less digits than its factorization.

21218457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41880 (or 41867 counting only the distinct ones).

The product of its digits is 4480, while the sum is 30.

The square root of 21218457 is about 4606.3496393565. The cubic root of 21218457 is about 276.8457959981.

Adding to 21218457 its reverse (75481212), we get a palindrome (96699669).

The spelling of 21218457 in words is "twenty-one million, two hundred eighteen thousand, four hundred fifty-seven".