21318640 has 40 divisors (see below), whose sum is σ = 56648160. Its totient is φ = 7309056.

The previous prime is 21318599. The next prime is 21318643. The reversal of 21318640 is 4681312.

It is a tau number, because it is divible by the number of its divisors (40).

It is a super-2 number, since 2×21318640² = 908968822899200, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21318643) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18475 + ... + 19594.

It is an arithmetic number, because the mean of its divisors is an integer number (1416204).

Almost surely, 2^21318640 is an apocalyptic number.

21318640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21318640 is an abundant number, since it is smaller than the sum of its proper divisors (35329520).

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

21318640 is a wasteful number, since it uses less digits than its factorization.

21318640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38089 (or 38083 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 25.

The square root of 21318640 is about 4617.2112795496. The cubic root of 21318640 is about 277.2808214392.

Adding to 21318640 its reverse (4681312), we get a palindrome (25999952).

The spelling of 21318640 in words is "twenty-one million, three hundred eighteen thousand, six hundred forty".