21991200 has 432 divisors, whose sum is σ = 96181344. Its totient is φ = 4300800.

The previous prime is 21991199. The next prime is 21991219. The reversal of 21991200 is 219912.

It is a super-2 number, since 2×21991200² = 967225754880000, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 1293592 + ... + 1293608.

It is an arithmetic number, because the mean of its divisors is an integer number (222642).

Almost surely, 2^21991200 is an apocalyptic number.

21991200 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 21991200, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (48090672).

21991200 is an abundant number, since it is smaller than the sum of its proper divisors (74190144).

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

21991200 is a wasteful number, since it uses less digits than its factorization.

21991200 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 65 (or 45 counting only the distinct ones).

The product of its (nonzero) digits is 324, while the sum is 24.

The square root of 21991200 is about 4689.4775828444. The cubic root of 21991200 is about 280.1665675586.

Multiplying 21991200 by its reverse (219912), we get a square (4836128774400 = 2199120²).

21991200 divided by its reverse (219912) gives a square (100 = 10²).

It can be divided in two parts, 219 and 91200, that added together give a palindrome (91419).

The spelling of 21991200 in words is "twenty-one million, nine hundred ninety-one thousand, two hundred".