21218237 has 4 divisors (see below), whose sum is σ = 21234240. Its totient is φ = 21202236.

The previous prime is 21218233. The next prime is 21218251. The reversal of 21218237 is 73281212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21218237 - 2² = 21218233 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21218233) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5813 + ... + 8730.

It is an arithmetic number, because the mean of its divisors is an integer number (5308560).

Almost surely, 2^21218237 is an apocalyptic number.

It is an amenable number.

21218237 is a deficient number, since it is larger than the sum of its proper divisors (16003).

21218237 is a wasteful number, since it uses less digits than its factorization.

21218237 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16002.

The product of its digits is 1344, while the sum is 26.

The square root of 21218237 is about 4606.3257592142. The cubic root of 21218237 is about 276.8448391851.

Adding to 21218237 its reverse (73281212), we get a palindrome (94499449).

The spelling of 21218237 in words is "twenty-one million, two hundred eighteen thousand, two hundred thirty-seven".