21218772 has 12 divisors (see below), whose sum is σ = 49510496. Its totient is φ = 7072920.

The previous prime is 21218759. The next prime is 21218777. The reversal of 21218772 is 27781212.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (12).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21218777) 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, 884104 + ... + 884127.

Almost surely, 2^21218772 is an apocalyptic number.

It is an amenable number.

21218772 is an abundant number, since it is smaller than the sum of its proper divisors (28291724).

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

21218772 is a wasteful number, since it uses less digits than its factorization.

21218772 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1768238 (or 1768236 counting only the distinct ones).

The product of its digits is 3136, while the sum is 30.

The square root of 21218772 is about 4606.3838311630. The cubic root of 21218772 is about 276.8471659688.

Adding to 21218772 its reverse (27781212), we get a palindrome (48999984).

The spelling of 21218772 in words is "twenty-one million, two hundred eighteen thousand, seven hundred seventy-two".