21640066 has 24 divisors (see below), whose sum is σ = 37920960. Its totient is φ = 9234792.

The previous prime is 21640063. The next prime is 21640067. The reversal of 21640066 is 66004612.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21640066.

It is not an unprimeable number, because it can be changed into a prime (21640063) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 42771 + ... + 43273.

It is an arithmetic number, because the mean of its divisors is an integer number (1580040).

Almost surely, 2^21640066 is an apocalyptic number.

21640066 is a deficient number, since it is larger than the sum of its proper divisors (16280894).

21640066 is a wasteful number, since it uses less digits than its factorization.

21640066 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 958 (or 951 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 25.

The square root of 21640066 is about 4651.8884337439. Note that the first 3 decimals coincide. The cubic root of 21640066 is about 278.6674180083.

Adding to 21640066 its reverse (66004612), we get a palindrome (87644678).

The spelling of 21640066 in words is "twenty-one million, six hundred forty thousand, sixty-six".