21321557 has 2 divisors, whose sum is σ = 21321558. Its totient is φ = 21321556.

The previous prime is 21321551. The next prime is 21321563. The reversal of 21321557 is 75512312.

It is a balanced prime because it is at equal distance from previous prime (21321551) and next prime (21321563).

It can be written as a sum of positive squares in only one way, i.e., 19989841 + 1331716 = 4471^2 + 1154^2 .

It is a cyclic number.

It is not a de Polignac number, because 21321557 - 2⁶ = 21321493 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 (21321551) 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, 10660778 + 10660779.

It is an arithmetic number, because the mean of its divisors is an integer number (10660779).

Almost surely, 2^21321557 is an apocalyptic number.

It is an amenable number.

21321557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21321557 is an equidigital number, since it uses as much as digits as its factorization.

21321557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2100, while the sum is 26.

The square root of 21321557 is about 4617.5271520588. The cubic root of 21321557 is about 277.2934675128.

Adding to 21321557 its reverse (75512312), we get a palindrome (96833869).

The spelling of 21321557 in words is "twenty-one million, three hundred twenty-one thousand, five hundred fifty-seven".