21245557 has 2 divisors, whose sum is σ = 21245558. Its totient is φ = 21245556.

The previous prime is 21245533. The next prime is 21245561. The reversal of 21245557 is 75554212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18714276 + 2531281 = 4326^2 + 1591^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21245557 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21245057) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10622778 + 10622779.

It is an arithmetic number, because the mean of its divisors is an integer number (10622779).

Almost surely, 2^21245557 is an apocalyptic number.

It is an amenable number.

21245557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21245557 is an equidigital number, since it uses as much as digits as its factorization.

21245557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 14000, while the sum is 31.

The square root of 21245557 is about 4609.2902924420. The cubic root of 21245557 is about 276.9636074125.

Adding to 21245557 its reverse (75554212), we get a palindrome (96799769).

The spelling of 21245557 in words is "twenty-one million, two hundred forty-five thousand, five hundred fifty-seven".