21597557 has 2 divisors, whose sum is σ = 21597558. Its totient is φ = 21597556.

The previous prime is 21597551. The next prime is 21597559. The reversal of 21597557 is 75579512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19018321 + 2579236 = 4361^2 + 1606^2 .

It is a cyclic number.

It is not a de Polignac number, because 21597557 - 2²⁴ = 4820341 is a prime.

Together with 21597559, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21597551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10798778 + 10798779.

It is an arithmetic number, because the mean of its divisors is an integer number (10798779).

Almost surely, 2^21597557 is an apocalyptic number.

It is an amenable number.

21597557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21597557 is an equidigital number, since it uses as much as digits as its factorization.

21597557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 110250, while the sum is 41.

The square root of 21597557 is about 4647.3171830638. The cubic root of 21597557 is about 278.4848301751.

The spelling of 21597557 in words is "twenty-one million, five hundred ninety-seven thousand, five hundred fifty-seven".