21660000 has 180 divisors, whose sum is σ = 74985372. Its totient is φ = 5472000.

The previous prime is 21659999. The next prime is 21660007. The reversal of 21660000 is 6612.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21660007) by changing a digit.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 1139991 + ... + 1140009.

Almost surely, 2^21660000 is an apocalyptic number.

21660000 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 21660000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37492686).

21660000 is an abundant number, since it is smaller than the sum of its proper divisors (53325372).

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

21660000 is an equidigital number, since it uses as much as digits as its factorization.

21660000 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71 (or 29 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 15.

The square root of 21660000 is about 4654.0305112880. The cubic root of 21660000 is about 278.7529576660.

Adding to 21660000 its reverse (6612), we get a palindrome (21666612).

It can be divided in two parts, 216 and 60000, that multiplied together give a 4-th power (12960000 = 60⁴).

The spelling of 21660000 in words is "twenty-one million, six hundred sixty thousand".