21432209 has 6 divisors (see below), whose sum is σ = 22619970. Its totient is φ = 20303856.

The previous prime is 21432199. The next prime is 21432211. The reversal of 21432209 is 90223412.

It can be written as a sum of positive squares in only one way, i.e., 12759184 + 8673025 = 3572^2 + 2945^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21432209 is a prime.

It is a super-3 number, since 3×21432209³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21432239) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 29324 + ... + 30045.

It is an arithmetic number, because the mean of its divisors is an integer number (3769995).

Almost surely, 2^21432209 is an apocalyptic number.

It is an amenable number.

21432209 is a deficient number, since it is larger than the sum of its proper divisors (1187761).

21432209 is an equidigital number, since it uses as much as digits as its factorization.

21432209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 59407 (or 59388 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 23.

The square root of 21432209 is about 4629.4933848100. The cubic root of 21432209 is about 277.7723279583.

It can be divided in two parts, 214 and 32209, that added together give a palindrome (32423).

The spelling of 21432209 in words is "twenty-one million, four hundred thirty-two thousand, two hundred nine".