21005129 has 2 divisors, whose sum is σ = 21005130. Its totient is φ = 21005128.

The previous prime is 21005123. The next prime is 21005143. The reversal of 21005129 is 92150012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20457529 + 547600 = 4523^2 + 740^2 .

It is a cyclic number.

It is not a de Polignac number, because 21005129 - 2¹² = 21001033 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21005129.

It is not a weakly prime, because it can be changed into another prime (21005123) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10502564 + 10502565.

It is an arithmetic number, because the mean of its divisors is an integer number (10502565).

Almost surely, 2^21005129 is an apocalyptic number.

It is an amenable number.

21005129 is a deficient number, since it is larger than the sum of its proper divisors (1).

21005129 is an equidigital number, since it uses as much as digits as its factorization.

21005129 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 180, while the sum is 20.

The square root of 21005129 is about 4583.1352805694. The cubic root of 21005129 is about 275.9148769559.

The spelling of 21005129 in words is "twenty-one million, five thousand, one hundred twenty-nine".