21000115 has 4 divisors (see below), whose sum is σ = 25200144. Its totient is φ = 16800088.

The previous prime is 21000103. The next prime is 21000121. The reversal of 21000115 is 51100012.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21000115 is a prime.

It is a Duffinian 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 in 3 ways as a sum of consecutive naturals, for example, 2100007 + ... + 2100016.

It is an arithmetic number, because the mean of its divisors is an integer number (6300036).

Almost surely, 2^21000115 is an apocalyptic number.

21000115 is a deficient number, since it is larger than the sum of its proper divisors (4200029).

21000115 is an equidigital number, since it uses as much as digits as its factorization.

21000115 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4200028.

The product of its (nonzero) digits is 10, while the sum is 10.

The square root of 21000115 is about 4582.5882424674. The cubic root of 21000115 is about 275.8929212503.

Adding to 21000115 its reverse (51100012), we get a palindrome (72100127).

It can be divided in two parts, 21000 and 115, that added together give a triangular number (21115 = T₂₀₅).

The spelling of 21000115 in words is "twenty-one million, one hundred fifteen", and thus it is an aban number.