21138989 has 2 divisors, whose sum is σ = 21138990. Its totient is φ = 21138988.

The previous prime is 21138983. The next prime is 21139009. The reversal of 21138989 is 98983112.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21114025 + 24964 = 4595^2 + 158^2 .

It is a cyclic number.

It is not a de Polignac number, because 21138989 - 2¹⁶ = 21073453 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21138983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10569494 + 10569495.

It is an arithmetic number, because the mean of its divisors is an integer number (10569495).

Almost surely, 2^21138989 is an apocalyptic number.

It is an amenable number.

21138989 is a deficient number, since it is larger than the sum of its proper divisors (1).

21138989 is an equidigital number, since it uses as much as digits as its factorization.

21138989 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 31104, while the sum is 41.

The square root of 21138989 is about 4597.7156284398. The cubic root of 21138989 is about 276.4997465736.

The spelling of 21138989 in words is "twenty-one million, one hundred thirty-eight thousand, nine hundred eighty-nine".