21205670 has 32 divisors (see below), whose sum is σ = 40007520. Its totient is φ = 8081920.

The previous prime is 21205663. The next prime is 21205687. The reversal of 21205670 is 7650212.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 23630 + ... + 24510.

It is an arithmetic number, because the mean of its divisors is an integer number (1250235).

Almost surely, 2^21205670 is an apocalyptic number.

21205670 is a deficient number, since it is larger than the sum of its proper divisors (18801850).

21205670 is a wasteful number, since it uses less digits than its factorization.

21205670 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1000.

The product of its (nonzero) digits is 840, while the sum is 23.

The square root of 21205670 is about 4604.9614547790. The cubic root of 21205670 is about 276.7901724350.

Adding to 21205670 its reverse (7650212), we get a palindrome (28855882).

The spelling of 21205670 in words is "twenty-one million, two hundred five thousand, six hundred seventy".