21399966 has 72 divisors (see below), whose sum is σ = 56819880. Its totient is φ = 5787936.

The previous prime is 21399953. The next prime is 21399967. The reversal of 21399966 is 66999312.

It is a happy number.

It is a nude number because it is divisible by every one of its digits.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21399967) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 16120 + ... + 17396.

It is an arithmetic number, because the mean of its divisors is an integer number (789165).

Almost surely, 2^21399966 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21399966, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28409940).

21399966 is an abundant number, since it is smaller than the sum of its proper divisors (35419914).

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

21399966 is a wasteful number, since it uses less digits than its factorization.

21399966 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1318 (or 1308 counting only the distinct ones).

The product of its digits is 157464, while the sum is 45.

The square root of 21399966 is about 4626.0097276162. The cubic root of 21399966 is about 277.6329628214.

The spelling of 21399966 in words is "twenty-one million, three hundred ninety-nine thousand, nine hundred sixty-six".