21212749 has 2 divisors, whose sum is σ = 21212750. Its totient is φ = 21212748.

The previous prime is 21212731. The next prime is 21212777. The reversal of 21212749 is 94721212.

It is an a-pointer prime, because the next prime (21212777) can be obtained adding 21212749 to its sum of digits (28).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21206025 + 6724 = 4605^2 + 82^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212749 - 2²¹ = 19115597 is a prime.

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21212449) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606374 + 10606375.

It is an arithmetic number, because the mean of its divisors is an integer number (10606375).

Almost surely, 2^21212749 is an apocalyptic number.

It is an amenable number.

21212749 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212749 is an equidigital number, since it uses as much as digits as its factorization.

21212749 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 28.

The square root of 21212749 is about 4605.7300181404. The cubic root of 21212749 is about 276.8209689097.

The spelling of 21212749 in words is "twenty-one million, two hundred twelve thousand, seven hundred forty-nine".