21212766 has 40 divisors (see below), whose sum is σ = 48830760. Its totient is φ = 6877872.

The previous prime is 21212749. The next prime is 21212777. The reversal of 21212766 is 66721212.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 4225 + ... + 7763.

It is an arithmetic number, because the mean of its divisors is an integer number (1220769).

Almost surely, 2^21212766 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21212766, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24415380).

21212766 is an abundant number, since it is smaller than the sum of its proper divisors (27617994).

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

21212766 is a wasteful number, since it uses less digits than its factorization.

21212766 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3590 (or 3581 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21212766 is about 4605.7318636673. The cubic root of 21212766 is about 276.8210428582.

Adding to 21212766 its reverse (66721212), we get a palindrome (87933978).

The spelling of 21212766 in words is "twenty-one million, two hundred twelve thousand, seven hundred sixty-six".