21788257 has 4 divisors (see below), whose sum is σ = 22491136. Its totient is φ = 21085380.

The previous prime is 21788233. The next prime is 21788293. The reversal of 21788257 is 75288712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21788257 - 2¹¹ = 21786209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21788297) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 351393 + ... + 351454.

It is an arithmetic number, because the mean of its divisors is an integer number (5622784).

Almost surely, 2^21788257 is an apocalyptic number.

It is an amenable number.

21788257 is a deficient number, since it is larger than the sum of its proper divisors (702879).

21788257 is an equidigital number, since it uses as much as digits as its factorization.

21788257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 702878.

The product of its digits is 62720, while the sum is 40.

The square root of 21788257 is about 4667.7893054421. The cubic root of 21788257 is about 279.3020755834.

The spelling of 21788257 in words is "twenty-one million, seven hundred eighty-eight thousand, two hundred fifty-seven".