21991880 has 32 divisors (see below), whose sum is σ = 52394040. Its totient is φ = 8279040.

The previous prime is 21991847. The next prime is 21991883. The reversal of 21991880 is 8819912.

It can be written as a sum of positive squares in 4 ways, for example, as 16048036 + 5943844 = 4006^2 + 2438^2 .

It is a super-3 number, since 3×21991880³ (a number of 23 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (21991883) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15491 + ... + 16850.

Almost surely, 2^21991880 is an apocalyptic number.

21991880 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21991880 is an abundant number, since it is smaller than the sum of its proper divisors (30402160).

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

21991880 is a wasteful number, since it uses less digits than its factorization.

21991880 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32369 (or 32365 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 38.

The square root of 21991880 is about 4689.5500850295. The cubic root of 21991880 is about 280.1694552486.

The spelling of 21991880 in words is "twenty-one million, nine hundred ninety-one thousand, eight hundred eighty".