21021989 has 2 divisors, whose sum is σ = 21021990. Its totient is φ = 21021988.

The previous prime is 21021953. The next prime is 21021997. The reversal of 21021989 is 98912012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19936225 + 1085764 = 4465^2 + 1042^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21021989 is a prime.

It is a super-2 number, since 2×21021989² = 883848043032242, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21021389) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510994 + 10510995.

It is an arithmetic number, because the mean of its divisors is an integer number (10510995).

Almost surely, 2^21021989 is an apocalyptic number.

It is an amenable number.

21021989 is a deficient number, since it is larger than the sum of its proper divisors (1).

21021989 is an equidigital number, since it uses as much as digits as its factorization.

21021989 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2592, while the sum is 32.

The square root of 21021989 is about 4584.9742638318. The cubic root of 21021989 is about 275.9886792598.

The spelling of 21021989 in words is "twenty-one million, twenty-one thousand, nine hundred eighty-nine".