21220657 has 4 divisors (see below), whose sum is σ = 21738276. Its totient is φ = 20703040.

The previous prime is 21220649. The next prime is 21220687. The reversal of 21220657 is 75602212.

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 4704561 + 16516096 = 2169^2 + 4064^2 .

It is a cyclic number.

It is not a de Polignac number, because 21220657 - 2³ = 21220649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21220627) 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, 258748 + ... + 258829.

It is an arithmetic number, because the mean of its divisors is an integer number (5434569).

Almost surely, 2^21220657 is an apocalyptic number.

It is an amenable number.

21220657 is a deficient number, since it is larger than the sum of its proper divisors (517619).

21220657 is an equidigital number, since it uses as much as digits as its factorization.

21220657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 517618.

The product of its (nonzero) digits is 1680, while the sum is 25.

The square root of 21220657 is about 4606.5884339715. The cubic root of 21220657 is about 276.8553637643.

Adding to 21220657 its reverse (75602212), we get a palindrome (96822869).

The spelling of 21220657 in words is "twenty-one million, two hundred twenty thousand, six hundred fifty-seven".