21005273 has 4 divisors (see below), whose sum is σ = 21213348. Its totient is φ = 20797200.

The previous prime is 21005269. The next prime is 21005291. The reversal of 21005273 is 37250012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 18088009 + 2917264 = 4253^2 + 1708^2 .

It is a cyclic number.

It is not a de Polignac number, because 21005273 - 2² = 21005269 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21005293) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 103886 + ... + 104087.

It is an arithmetic number, because the mean of its divisors is an integer number (5303337).

Almost surely, 2^21005273 is an apocalyptic number.

It is an amenable number.

21005273 is a deficient number, since it is larger than the sum of its proper divisors (208075).

21005273 is a wasteful number, since it uses less digits than its factorization.

21005273 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 208074.

The product of its (nonzero) digits is 420, while the sum is 20.

The square root of 21005273 is about 4583.1509903122. The cubic root of 21005273 is about 275.9155074631.

Adding to 21005273 its reverse (37250012), we get a palindrome (58255285).

The spelling of 21005273 in words is "twenty-one million, five thousand, two hundred seventy-three".