21090249 has 6 divisors (see below), whose sum is σ = 30463706. Its totient is φ = 14060160.

The previous prime is 21090239. The next prime is 21090269. The reversal of 21090249 is 94209012.

It can be written as a sum of positive squares in only one way, i.e., 19316025 + 1774224 = 4395^2 + 1332^2 .

It is not a de Polignac number, because 21090249 - 2⁸ = 21089993 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21090239) 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 in 5 ways as a sum of consecutive naturals, for example, 1171672 + ... + 1171689.

Almost surely, 2^21090249 is an apocalyptic number.

It is an amenable number.

21090249 is a deficient number, since it is larger than the sum of its proper divisors (9373457).

21090249 is a wasteful number, since it uses less digits than its factorization.

21090249 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2343367 (or 2343364 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21090249 is about 4592.4121112984. The cubic root of 21090249 is about 276.2870752775.

The spelling of 21090249 in words is "twenty-one million, ninety thousand, two hundred forty-nine".