21180205 has 8 divisors (see below), whose sum is σ = 25668504. Its totient is φ = 16776000.

The previous prime is 21180197. The next prime is 21180227. The reversal of 21180205 is 50208112.

It can be written as a sum of positive squares in 4 ways, for example, as 1705636 + 19474569 = 1306^2 + 4413^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21180205 - 2³ = 21180197 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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 in 7 ways as a sum of consecutive naturals, for example, 20466 + ... + 21475.

It is an arithmetic number, because the mean of its divisors is an integer number (3208563).

Almost surely, 2^21180205 is an apocalyptic number.

It is an amenable number.

21180205 is a deficient number, since it is larger than the sum of its proper divisors (4488299).

21180205 is a wasteful number, since it uses less digits than its factorization.

21180205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42047.

The product of its (nonzero) digits is 160, while the sum is 19.

The square root of 21180205 is about 4602.1956716333. The cubic root of 21180205 is about 276.6793328180.

Adding to 21180205 its reverse (50208112), we get a palindrome (71388317).

The spelling of 21180205 in words is "twenty-one million, one hundred eighty thousand, two hundred five".