21137640 has 64 divisors (see below), whose sum is σ = 63720000. Its totient is φ = 5609472.

The previous prime is 21137609. The next prime is 21137657. The reversal of 21137640 is 4673112.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21137640.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 42111 + ... + 42609.

It is an arithmetic number, because the mean of its divisors is an integer number (995625).

Almost surely, 2^21137640 is an apocalyptic number.

21137640 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 21137640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31860000).

21137640 is an abundant number, since it is smaller than the sum of its proper divisors (42582360).

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

21137640 is a wasteful number, since it uses less digits than its factorization.

21137640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 866 (or 862 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 24.

The square root of 21137640 is about 4597.5689228113. The cubic root of 21137640 is about 276.4938647708.

The spelling of 21137640 in words is "twenty-one million, one hundred thirty-seven thousand, six hundred forty".