21009203 has 4 divisors (see below), whose sum is σ = 21028608. Its totient is φ = 20989800.

The previous prime is 21009199. The next prime is 21009211. The reversal of 21009203 is 30290012.

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

It is a cyclic number.

It is not a de Polignac number, because 21009203 - 2² = 21009199 is a prime.

It is a super-2 number, since 2×21009203² = 882773221390418, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21009283) 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, 7976 + ... + 10277.

It is an arithmetic number, because the mean of its divisors is an integer number (5257152).

Almost surely, 2^21009203 is an apocalyptic number.

21009203 is a deficient number, since it is larger than the sum of its proper divisors (19405).

21009203 is a wasteful number, since it uses less digits than its factorization.

21009203 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19404.

The product of its (nonzero) digits is 108, while the sum is 17.

The square root of 21009203 is about 4583.5797145899. The cubic root of 21009203 is about 275.9327139414.

Adding to 21009203 its reverse (30290012), we get a palindrome (51299215).

It can be divided in two parts, 21009 and 203, that added together give a palindrome (21212).

The spelling of 21009203 in words is "twenty-one million, nine thousand, two hundred three".