21218387 has 2 divisors, whose sum is σ = 21218388. Its totient is φ = 21218386.

The previous prime is 21218359. The next prime is 21218413. The reversal of 21218387 is 78381212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21218387 - 2¹⁴ = 21202003 is a prime.

It is a Chen prime.

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

It is not a weakly prime, because it can be changed into another prime (21218317) 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 as a sum of consecutive naturals, namely, 10609193 + 10609194.

It is an arithmetic number, because the mean of its divisors is an integer number (10609194).

Almost surely, 2^21218387 is an apocalyptic number.

21218387 is a deficient number, since it is larger than the sum of its proper divisors (1).

21218387 is an equidigital number, since it uses as much as digits as its factorization.

21218387 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5376, while the sum is 32.

The square root of 21218387 is about 4606.3420411428. The cubic root of 21218387 is about 276.8454915584.

Adding to 21218387 its reverse (78381212), we get a palindrome (99599599).

The spelling of 21218387 in words is "twenty-one million, two hundred eighteen thousand, three hundred eighty-seven".