21668257 has 4 divisors (see below), whose sum is σ = 23335060. Its totient is φ = 20001456.

The previous prime is 21668221. The next prime is 21668261. The reversal of 21668257 is 75286612.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10751841 + 10916416 = 3279^2 + 3304^2 .

It is a cyclic number.

It is not a de Polignac number, because 21668257 - 2¹¹ = 21666209 is a prime.

It is a super-2 number, since 2×21668257² = 939026722836098, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21668267) 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, 833382 + ... + 833407.

It is an arithmetic number, because the mean of its divisors is an integer number (5833765).

Almost surely, 2^21668257 is an apocalyptic number.

It is an amenable number.

21668257 is a deficient number, since it is larger than the sum of its proper divisors (1666803).

21668257 is a wasteful number, since it uses less digits than its factorization.

21668257 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1666802.

The product of its digits is 40320, while the sum is 37.

The square root of 21668257 is about 4654.9175073249. The cubic root of 21668257 is about 278.7883742674.

The spelling of 21668257 in words is "twenty-one million, six hundred sixty-eight thousand, two hundred fifty-seven".