21025 has 9 divisors (see below), whose sum is σ = 27001. Its totient is φ = 16240.

The previous prime is 21023. The next prime is 21031. The reversal of 21025 is 52012.

21025 = T₁₄₄ + T₁₄₅.

The square root of 21025 is 145.

It is a perfect power (a square), and thus also a powerful number.

21025 is nontrivially palindromic in base 12.

It can be written as a sum of positive squares in 4 ways, for example, as 289 + 20736 = 17^2 + 144^2 .

It is not a de Polignac number, because 21025 - 2¹ = 21023 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13 and base 16.

It is not an unprimeable number, because it can be changed into a prime (21023) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 711 + ... + 739.

2²¹⁰²⁵ is an apocalyptic number.

21025 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21025 is the 145-th square number.

21025 is the 73-rd centered octagonal number.

It is an amenable number.

21025 is a deficient number, since it is larger than the sum of its proper divisors (5976).

21025 is an equidigital number, since it uses as much as digits as its factorization.

21025 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 68 (or 34 counting only the distinct ones).

The product of its (nonzero) digits is 20, while the sum is 10.

The cubic root of 21025 is about 27.6001855340.

Adding to 21025 its reverse (52012), we get a palindrome (73037).

The spelling of 21025 in words is "twenty-one thousand, twenty-five".