21015518 has 4 divisors (see below), whose sum is σ = 31523280. Its totient is φ = 10507758.

The previous prime is 21015497. The next prime is 21015523. The reversal of 21015518 is 81551012.

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

It is a junction number, because it is equal to n+sod(n) for n = 21015493 and 21015502.

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 as a sum of consecutive naturals, namely, 5253878 + ... + 5253881.

It is an arithmetic number, because the mean of its divisors is an integer number (7880820).

Almost surely, 2^21015518 is an apocalyptic number.

21015518 is a deficient number, since it is larger than the sum of its proper divisors (10507762).

21015518 is a wasteful number, since it uses less digits than its factorization.

21015518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10507761.

The product of its (nonzero) digits is 400, while the sum is 23.

The square root of 21015518 is about 4584.2685348919. The cubic root of 21015518 is about 275.9603580256.

The spelling of 21015518 in words is "twenty-one million, fifteen thousand, five hundred eighteen".