21311640 has 128 divisors (see below), whose sum is σ = 81216000. Its totient is φ = 4869504.

The previous prime is 21311629. The next prime is 21311683. The reversal of 21311640 is 4611312.

It is a happy number.

21311640 is a `hidden beast` number, since 2 + 13 + 11 + 640 = 666.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 6151 + ... + 8969.

It is an arithmetic number, because the mean of its divisors is an integer number (634500).

Almost surely, 2^21311640 is an apocalyptic number.

21311640 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 21311640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40608000).

21311640 is an abundant number, since it is smaller than the sum of its proper divisors (59904360).

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

21311640 is a wasteful number, since it uses less digits than its factorization.

21311640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2846 (or 2836 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 18.

The square root of 21311640 is about 4616.4531839931. The cubic root of 21311640 is about 277.2504696246.

Adding to 21311640 its reverse (4611312), we get a palindrome (25922952).

The spelling of 21311640 in words is "twenty-one million, three hundred eleven thousand, six hundred forty".