21102640 has 80 divisors (see below), whose sum is σ = 53621568. Its totient is φ = 7676928.

The previous prime is 21102623. The next prime is 21102643. The reversal of 21102640 is 4620112.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (16).

It is not an unprimeable number, because it can be changed into a prime (21102643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 107022 + ... + 107218.

Almost surely, 2^21102640 is an apocalyptic number.

21102640 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 21102640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26810784).

21102640 is an abundant number, since it is smaller than the sum of its proper divisors (32518928).

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

21102640 is a wasteful number, since it uses less digits than its factorization.

21102640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 326 (or 320 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 16.

The square root of 21102640 is about 4593.7609863814. The cubic root of 21102640 is about 276.3411729937.

Adding to 21102640 its reverse (4620112), we get a palindrome (25722752).

The spelling of 21102640 in words is "twenty-one million, one hundred two thousand, six hundred forty".