21121800 has 192 divisors, whose sum is σ = 77137920. Its totient is φ = 4680960.

The previous prime is 21121781. The next prime is 21121811. The reversal of 21121800 is 812112.

It is a super-2 number, since 2×21121800² = 892260870480000, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 21121800.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 197347 + ... + 197453.

It is an arithmetic number, because the mean of its divisors is an integer number (401760).

Almost surely, 2^21121800 is an apocalyptic number.

21121800 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 21121800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38568960).

21121800 is an abundant number, since it is smaller than the sum of its proper divisors (56016120).

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

21121800 is a wasteful number, since it uses less digits than its factorization.

21121800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 180 (or 171 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 15.

The square root of 21121800 is about 4595.8459504209. The cubic root of 21121800 is about 276.4247817310.

Adding to 21121800 its reverse (812112), we get a palindrome (21933912).

The spelling of 21121800 in words is "twenty-one million, one hundred twenty-one thousand, eight hundred".