21001549 has 2 divisors, whose sum is σ = 21001550. Its totient is φ = 21001548.

The previous prime is 21001531. The next prime is 21001559. The reversal of 21001549 is 94510012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 12299049 + 8702500 = 3507^2 + 2950^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001549 - 2⁹ = 21001037 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 (21001529) 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, 10500774 + 10500775.

It is an arithmetic number, because the mean of its divisors is an integer number (10500775).

Almost surely, 2^21001549 is an apocalyptic number.

It is an amenable number.

21001549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001549 is an equidigital number, since it uses as much as digits as its factorization.

21001549 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 360, while the sum is 22.

The square root of 21001549 is about 4582.7447015953. The cubic root of 21001549 is about 275.8992009214.

The spelling of 21001549 in words is "twenty-one million, one thousand, five hundred forty-nine".