21218385 has 16 divisors (see below), whose sum is σ = 34672896. Its totient is φ = 11075328.

The previous prime is 21218359. The next prime is 21218387. The reversal of 21218385 is 58381212.

21218385 = T₃₀₂ + T₃₀₃ + ... + T₅₃₆.

It is not a de Polignac number, because 21218385 - 2⁶ = 21218321 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (21218387) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 14344 + ... + 15753.

It is an arithmetic number, because the mean of its divisors is an integer number (2167056).

Almost surely, 2^21218385 is an apocalyptic number.

It is an amenable number.

21218385 is a deficient number, since it is larger than the sum of its proper divisors (13454511).

21218385 is a wasteful number, since it uses less digits than its factorization.

21218385 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30152.

The product of its digits is 3840, while the sum is 30.

The square root of 21218385 is about 4606.3418240508. The cubic root of 21218385 is about 276.8454828601.

Adding to 21218385 its reverse (58381212), we get a palindrome (79599597).

The spelling of 21218385 in words is "twenty-one million, two hundred eighteen thousand, three hundred eighty-five".