21855015 has 80 divisors (see below), whose sum is σ = 48299328. Its totient is φ = 9206784.

The previous prime is 21855011. The next prime is 21855017. The reversal of 21855015 is 51055812.

It is not a de Polignac number, because 21855015 - 2² = 21855011 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a self number, because there is not a number n which added to its sum of digits gives 21855015.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21855011) by changing a digit.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 36559 + ... + 37151.

Almost surely, 2^21855015 is an apocalyptic number.

21855015 is an abundant number, since it is smaller than the sum of its proper divisors (26444313).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21855015 is a wasteful number, since it uses less digits than its factorization.

21855015 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 630 (or 621 counting only the distinct ones).

The product of its (nonzero) digits is 2000, while the sum is 27.

The square root of 21855015 is about 4674.9347589031. The cubic root of 21855015 is about 279.5870400521.

The spelling of 21855015 in words is "twenty-one million, eight hundred fifty-five thousand, fifteen".