21010640 has 80 divisors (see below), whose sum is σ = 59139072. Its totient is φ = 6776832.

The previous prime is 21010609. The next prime is 21010663. The reversal of 21010640 is 4601012.

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 (14).

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, 8417 + ... + 10623.

Almost surely, 2^21010640 is an apocalyptic number.

21010640 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 21010640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29569536).

21010640 is an abundant number, since it is smaller than the sum of its proper divisors (38128432).

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

21010640 is a wasteful number, since it uses less digits than its factorization.

21010640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2244 (or 2238 counting only the distinct ones).

The product of its (nonzero) digits is 48, while the sum is 14.

The square root of 21010640 is about 4583.7364671194. The cubic root of 21010640 is about 275.9390049348.

Adding to 21010640 its reverse (4601012), we get a palindrome (25611652).

The spelling of 21010640 in words is "twenty-one million, ten thousand, six hundred forty".