21042506 has 4 divisors (see below), whose sum is σ = 31563762. Its totient is φ = 10521252.

The previous prime is 21042491. The next prime is 21042533. The reversal of 21042506 is 60524012.

It is a happy number.

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., 18966025 + 2076481 = 4355^2 + 1441^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5260625 + ... + 5260628.

Almost surely, 2^21042506 is an apocalyptic number.

21042506 is a deficient number, since it is larger than the sum of its proper divisors (10521256).

21042506 is a wasteful number, since it uses less digits than its factorization.

21042506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10521255.

The product of its (nonzero) digits is 480, while the sum is 20.

The square root of 21042506 is about 4587.2111353196. The cubic root of 21042506 is about 276.0784363642.

Adding to 21042506 its reverse (60524012), we get a palindrome (81566518).

The spelling of 21042506 in words is "twenty-one million, forty-two thousand, five hundred six".