21109980 has 72 divisors (see below), whose sum is σ = 60985008. Its totient is φ = 5455872.

The previous prime is 21109973. The next prime is 21109987. The reversal of 21109980 is 8990112.

It is an interprime number because it is at equal distance from previous prime (21109973) and next prime (21109987).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21109987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 82012 + ... + 82268.

It is an arithmetic number, because the mean of its divisors is an integer number (847014).

Almost surely, 2^21109980 is an apocalyptic number.

21109980 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21109980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30492504).

21109980 is an abundant number, since it is smaller than the sum of its proper divisors (39875028).

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

21109980 is a wasteful number, since it uses less digits than its factorization.

21109980 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 343 (or 304 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 30.

The square root of 21109980 is about 4594.5598265775. The cubic root of 21109980 is about 276.3732086235.

It can be divided in two parts, 2110 and 9980, that added together give a triangular number (12090 = T₁₅₅).

The spelling of 21109980 in words is "twenty-one million, one hundred nine thousand, nine hundred eighty".