21003509 has 2 divisors, whose sum is σ = 21003510. Its totient is φ = 21003508.

The previous prime is 21003503. The next prime is 21003527. The reversal of 21003509 is 90530012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20448484 + 555025 = 4522^2 + 745^2 .

It is a cyclic number.

It is not a de Polignac number, because 21003509 - 2²⁰ = 19954933 is a prime.

It is a super-2 number, since 2×21003509² = 882294780626162, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21003503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501754 + 10501755.

It is an arithmetic number, because the mean of its divisors is an integer number (10501755).

Almost surely, 2^21003509 is an apocalyptic number.

It is an amenable number.

21003509 is a deficient number, since it is larger than the sum of its proper divisors (1).

21003509 is an equidigital number, since it uses as much as digits as its factorization.

21003509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 270, while the sum is 20.

The square root of 21003509 is about 4582.9585422519. The cubic root of 21003509 is about 275.9077835520.

It can be divided in two parts, 21003 and 509, that added together give a palindrome (21512).

The spelling of 21003509 in words is "twenty-one million, three thousand, five hundred nine".