21015506 has 4 divisors (see below), whose sum is σ = 31523262. Its totient is φ = 10507752.

The previous prime is 21015497. The next prime is 21015523. The reversal of 21015506 is 60551012.

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., 11621281 + 9394225 = 3409^2 + 3065^2 .

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, 5253875 + ... + 5253878.

Almost surely, 2^21015506 is an apocalyptic number.

21015506 is a deficient number, since it is larger than the sum of its proper divisors (10507756).

21015506 is a wasteful number, since it uses less digits than its factorization.

21015506 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10507755.

The product of its (nonzero) digits is 300, while the sum is 20.

The square root of 21015506 is about 4584.2672260679. The cubic root of 21015506 is about 275.9603055005.

Adding to 21015506 its reverse (60551012), we get a palindrome (81566518).

The spelling of 21015506 in words is "twenty-one million, fifteen thousand, five hundred six".