21212756 has 6 divisors (see below), whose sum is σ = 37122330. Its totient is φ = 10606376.

The previous prime is 21212749. The next prime is 21212777. The reversal of 21212756 is 65721212.

It can be written as a sum of positive squares in only one way, i.e., 17472400 + 3740356 = 4180^2 + 1934^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2651591 + ... + 2651598.

It is an arithmetic number, because the mean of its divisors is an integer number (6187055).

Almost surely, 2^21212756 is an apocalyptic number.

It is an amenable number.

21212756 is a deficient number, since it is larger than the sum of its proper divisors (15909574).

21212756 is a wasteful number, since it uses less digits than its factorization.

21212756 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5303193 (or 5303191 counting only the distinct ones).

The product of its digits is 1680, while the sum is 26.

The square root of 21212756 is about 4605.7307780633. The cubic root of 21212756 is about 276.8209993591.

Adding to 21212756 its reverse (65721212), we get a palindrome (86933968).

The spelling of 21212756 in words is "twenty-one million, two hundred twelve thousand, seven hundred fifty-six".