21129557 has 2 divisors, whose sum is σ = 21129558. Its totient is φ = 21129556.

The previous prime is 21129551. The next prime is 21129583. The reversal of 21129557 is 75592112.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19589476 + 1540081 = 4426^2 + 1241^2 .

It is a cyclic number.

It is not a de Polignac number, because 21129557 - 2¹⁴ = 21113173 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21129551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10564778 + 10564779.

It is an arithmetic number, because the mean of its divisors is an integer number (10564779).

Almost surely, 2^21129557 is an apocalyptic number.

It is an amenable number.

21129557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21129557 is an equidigital number, since it uses as much as digits as its factorization.

21129557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6300, while the sum is 32.

The square root of 21129557 is about 4596.6897872273. The cubic root of 21129557 is about 276.4586166724.

The spelling of 21129557 in words is "twenty-one million, one hundred twenty-nine thousand, five hundred fifty-seven".