21220387 has 4 divisors (see below), whose sum is σ = 21247056. Its totient is φ = 21193720.

The previous prime is 21220379. The next prime is 21220391. The reversal of 21220387 is 78302212.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21220387 - 2³ = 21220379 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21220327) 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 3 ways as a sum of consecutive naturals, for example, 12103 + ... + 13744.

It is an arithmetic number, because the mean of its divisors is an integer number (5311764).

Almost surely, 2^21220387 is an apocalyptic number.

21220387 is a deficient number, since it is larger than the sum of its proper divisors (26669).

21220387 is an equidigital number, since it uses as much as digits as its factorization.

21220387 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26668.

The product of its (nonzero) digits is 1344, while the sum is 25.

The square root of 21220387 is about 4606.5591280260. The cubic root of 21220387 is about 276.8541895740.

Adding to 21220387 its reverse (78302212), we get a palindrome (99522599).

The spelling of 21220387 in words is "twenty-one million, two hundred twenty thousand, three hundred eighty-seven".