21331640 has 32 divisors (see below), whose sum is σ = 52360560. Its totient is φ = 7756800.

The previous prime is 21331637. The next prime is 21331643. The reversal of 21331640 is 4613312.

It is an interprime number because it is at equal distance from previous prime (21331637) and next prime (21331643).

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21331643) 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, 23801 + ... + 24680.

Almost surely, 2^21331640 is an apocalyptic number.

21331640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21331640 is an abundant number, since it is smaller than the sum of its proper divisors (31028920).

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

21331640 is a wasteful number, since it uses less digits than its factorization.

21331640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48503 (or 48499 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 20.

The square root of 21331640 is about 4618.6188411689. The cubic root of 21331640 is about 277.3371714726.

Adding to 21331640 its reverse (4613312), we get a palindrome (25944952).

It can be divided in two parts, 2133 and 1640, that added together give a palindrome (3773).

The spelling of 21331640 in words is "twenty-one million, three hundred thirty-one thousand, six hundred forty".