21253705 has 8 divisors (see below), whose sum is σ = 27823104. Its totient is φ = 15457200.

The previous prime is 21253697. The next prime is 21253711. The reversal of 21253705 is 50735212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21253705 - 2³ = 21253697 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21253705.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 193161 + ... + 193270.

It is an arithmetic number, because the mean of its divisors is an integer number (3477888).

Almost surely, 2^21253705 is an apocalyptic number.

It is an amenable number.

21253705 is a deficient number, since it is larger than the sum of its proper divisors (6569399).

21253705 is a wasteful number, since it uses less digits than its factorization.

21253705 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 386447.

The product of its (nonzero) digits is 2100, while the sum is 25.

The square root of 21253705 is about 4610.1740748046. The cubic root of 21253705 is about 276.9990094974. Note that the first 3 decimals are identical.

Adding to 21253705 its reverse (50735212), we get a palindrome (71988917).

The spelling of 21253705 in words is "twenty-one million, two hundred fifty-three thousand, seven hundred five".