21000640 has 112 divisors (see below), whose sum is σ = 54132480. Its totient is φ = 7741440.

The previous prime is 21000613. The next prime is 21000673. The reversal of 21000640 is 4600012.

21000640 is nontrivially palindromic in base 3.

It is a self number, because there is not a number n which added to its sum of digits gives 21000640.

It is a congruent number.

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, 287644 + ... + 287716.

Almost surely, 2^21000640 is an apocalyptic number.

21000640 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 21000640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27066240).

21000640 is an abundant number, since it is smaller than the sum of its proper divisors (33131840).

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

21000640 is a wasteful number, since it uses less digits than its factorization.

21000640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 150 (or 140 counting only the distinct ones).

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21000640 is about 4582.6455241487. The cubic root of 21000640 is about 275.8952203263.

Adding to 21000640 its reverse (4600012), we get a palindrome (25600652).

The spelling of 21000640 in words is "twenty-one million, six hundred forty", and thus it is an aban number.