21780915 has 16 divisors (see below), whose sum is σ = 37530528. Its totient is φ = 10722816.

The previous prime is 21780907. The next prime is 21780917. The reversal of 21780915 is 51908712.

It is not a de Polignac number, because 21780915 - 2³ = 21780907 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21780917) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 55654 + ... + 56043.

It is an arithmetic number, because the mean of its divisors is an integer number (2345658).

Almost surely, 2^21780915 is an apocalyptic number.

21780915 is a deficient number, since it is larger than the sum of its proper divisors (15749613).

21780915 is a wasteful number, since it uses less digits than its factorization.

21780915 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 111718.

The product of its (nonzero) digits is 5040, while the sum is 33.

The square root of 21780915 is about 4667.0027855145. The cubic root of 21780915 is about 279.2706998716.

The spelling of 21780915 in words is "twenty-one million, seven hundred eighty thousand, nine hundred fifteen".