21165880 has 32 divisors (see below), whose sum is σ = 47790000. Its totient is φ = 8436736.

The previous prime is 21165871. The next prime is 21165883. The reversal of 21165880 is 8856112.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21165883) 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 7 ways as a sum of consecutive naturals, for example, 13371 + ... + 14869.

Almost surely, 2^21165880 is an apocalyptic number.

21165880 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21165880 is an abundant number, since it is smaller than the sum of its proper divisors (26624120).

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

21165880 is a wasteful number, since it uses less digits than its factorization.

21165880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1863 (or 1859 counting only the distinct ones).

The product of its (nonzero) digits is 3840, while the sum is 31.

The square root of 21165880 is about 4600.6390860401. The cubic root of 21165880 is about 276.6169424033.

It can be divided in two parts, 21 and 165880, that multiplied together give a triangular number (3483480 = T₂₆₃₉).

The spelling of 21165880 in words is "twenty-one million, one hundred sixty-five thousand, eight hundred eighty".