21726257 has 12 divisors (see below), whose sum is σ = 26090496. Its totient is φ = 18020520.

The previous prime is 21726251. The next prime is 21726311. The reversal of 21726257 is 75262712.

It is a de Polignac number, because none of the positive numbers 2^k-21726257 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21726251) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5633 + ... + 8670.

It is an arithmetic number, because the mean of its divisors is an integer number (2174208).

Almost surely, 2^21726257 is an apocalyptic number.

It is an amenable number.

21726257 is a deficient number, since it is larger than the sum of its proper divisors (4364239).

21726257 is a wasteful number, since it uses less digits than its factorization.

21726257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14348 (or 14341 counting only the distinct ones).

The product of its digits is 11760, while the sum is 32.

The square root of 21726257 is about 4661.1433146815. The cubic root of 21726257 is about 279.0368994074.

Adding to 21726257 its reverse (75262712), we get a palindrome (96988969).

It can be divided in two parts, 217 and 26257, that multiplied together give a square (5697769 = 2387²).

The spelling of 21726257 in words is "twenty-one million, seven hundred twenty-six thousand, two hundred fifty-seven".