21661200 has 180 divisors, whose sum is σ = 82153968. Its totient is φ = 5241600.

The previous prime is 21661183. The next prime is 21661223. The reversal of 21661200 is 216612.

It is a happy number.

21661200 is a `hidden beast` number, since 2 + 1 + 661 + 2 + 0 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (180).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 39327 + ... + 39873.

Almost surely, 2^21661200 is an apocalyptic number.

21661200 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 21661200, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41076984).

21661200 is an abundant number, since it is smaller than the sum of its proper divisors (60492768).

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

21661200 is a wasteful number, since it uses less digits than its factorization.

21661200 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 582 (or 568 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21661200 is about 4654.1594300153. The cubic root of 21661200 is about 278.7581053633.

Adding to 21661200 its reverse (216612), we get a palindrome (21877812).

Multiplying 21661200 by its reverse (216612), we get a square (4692075854400 = 2166120²).

21661200 divided by its reverse (216612) gives a square (100 = 10²).

It can be divided in two parts, 216 and 61200, that added together give a palindrome (61416).

The spelling of 21661200 in words is "twenty-one million, six hundred sixty-one thousand, two hundred".