21991980 has 48 divisors (see below), whose sum is σ = 62433504. Its totient is φ = 5783040.

The previous prime is 21991969. The next prime is 21991993. The reversal of 21991980 is 8919912.

It is a happy number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1870 + ... + 6890.

It is an arithmetic number, because the mean of its divisors is an integer number (1300698).

Almost surely, 2^21991980 is an apocalyptic number.

21991980 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 21991980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31216752).

21991980 is an abundant number, since it is smaller than the sum of its proper divisors (40441524).

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

21991980 is a wasteful number, since it uses less digits than its factorization.

21991980 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5106 (or 5104 counting only the distinct ones).

The product of its (nonzero) digits is 11664, while the sum is 39.

The square root of 21991980 is about 4689.5607470210. The cubic root of 21991980 is about 280.1698799038.

The spelling of 21991980 in words is "twenty-one million, nine hundred ninety-one thousand, nine hundred eighty".