21210506 has 4 divisors (see below), whose sum is σ = 31815762. Its totient is φ = 10605252.

The previous prime is 21210499. The next prime is 21210521. The reversal of 21210506 is 60501212.

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

It can be written as a sum of positive squares in only one way, i.e., 21077281 + 133225 = 4591^2 + 365^2 .

It is a Curzon 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 as a sum of consecutive naturals, namely, 5302625 + ... + 5302628.

Almost surely, 2^21210506 is an apocalyptic number.

21210506 is a deficient number, since it is larger than the sum of its proper divisors (10605256).

21210506 is a wasteful number, since it uses less digits than its factorization.

21210506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10605255.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 21210506 is about 4605.4865106740. The cubic root of 21210506 is about 276.8112117063.

Adding to 21210506 its reverse (60501212), we get a palindrome (81711718).

The spelling of 21210506 in words is "twenty-one million, two hundred ten thousand, five hundred six".