21251745 has 12 divisors (see below), whose sum is σ = 36836436. Its totient is φ = 11334240.

The previous prime is 21251731. The next prime is 21251773. The reversal of 21251745 is 54715212.

It can be written as a sum of positive squares in 2 ways, for example, as 2692881 + 18558864 = 1641^2 + 4308^2 .

It is not a de Polignac number, because 21251745 - 2⁷ = 21251617 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 236086 + ... + 236175.

It is an arithmetic number, because the mean of its divisors is an integer number (3069703).

Almost surely, 2^21251745 is an apocalyptic number.

It is an amenable number.

21251745 is a deficient number, since it is larger than the sum of its proper divisors (15584691).

21251745 is a wasteful number, since it uses less digits than its factorization.

21251745 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 472272 (or 472269 counting only the distinct ones).

The product of its digits is 2800, while the sum is 27.

The square root of 21251745 is about 4609.9614965854. The cubic root of 21251745 is about 276.9904943586.

Adding to 21251745 its reverse (54715212), we get a palindrome (75966957).

The spelling of 21251745 in words is "twenty-one million, two hundred fifty-one thousand, seven hundred forty-five".