21218712 has 32 divisors (see below), whose sum is σ = 53233200. Its totient is φ = 7048064.

The previous prime is 21218693. The next prime is 21218713. The reversal of 21218712 is 21781212.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21218713) 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 7 ways as a sum of consecutive naturals, for example, 6214 + ... + 9002.

Almost surely, 2^21218712 is an apocalyptic number.

It is an amenable number.

21218712 is an abundant number, since it is smaller than the sum of its proper divisors (32014488).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21218712 is a wasteful number, since it uses less digits than its factorization.

21218712 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3115 (or 3111 counting only the distinct ones).

The product of its digits is 448, while the sum is 24.

The square root of 21218712 is about 4606.3773184575. The cubic root of 21218712 is about 276.8469050231.

Adding to 21218712 its reverse (21781212), we get a palindrome (42999924).

Subtracting 21218712 from its reverse (21781212), we obtain a square (562500 = 750²).

The spelling of 21218712 in words is "twenty-one million, two hundred eighteen thousand, seven hundred twelve".