21075309 has 10 divisors (see below), whose sum is σ = 31482990. Its totient is φ = 14050152.

The previous prime is 21075283. The next prime is 21075347. The reversal of 21075309 is 90357012.

It can be written as a sum of positive squares in only one way, i.e., 19053225 + 2022084 = 4365^2 + 1422^2 .

It is not a de Polignac number, because 21075309 - 2⁷ = 21075181 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21075349) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 130014 + ... + 130175.

It is an arithmetic number, because the mean of its divisors is an integer number (3148299).

Almost surely, 2^21075309 is an apocalyptic number.

It is an amenable number.

21075309 is a deficient number, since it is larger than the sum of its proper divisors (10407681).

21075309 is an equidigital number, since it uses as much as digits as its factorization.

21075309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 260201 (or 260192 counting only the distinct ones).

The product of its (nonzero) digits is 1890, while the sum is 27.

The square root of 21075309 is about 4590.7852269519. The cubic root of 21075309 is about 276.2218207301.

It can be divided in two parts, 2 and 1075309, that added together give a triangular number (1075311 = T₁₄₆₆).

The spelling of 21075309 in words is "twenty-one million, seventy-five thousand, three hundred nine".