21501640 has 64 divisors (see below), whose sum is σ = 50232960. Its totient is φ = 8279040.

The previous prime is 21501593. The next prime is 21501643. The reversal of 21501640 is 4610512.

It is not an unprimeable number, because it can be changed into a prime (21501643) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 190224 + ... + 190336.

It is an arithmetic number, because the mean of its divisors is an integer number (784890).

Almost surely, 2^21501640 is an apocalyptic number.

21501640 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 21501640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25116480).

21501640 is an abundant number, since it is smaller than the sum of its proper divisors (28731320).

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

21501640 is a wasteful number, since it uses less digits than its factorization.

21501640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 262 (or 258 counting only the distinct ones).

The product of its (nonzero) digits is 240, while the sum is 19.

The square root of 21501640 is about 4636.9860901236. The cubic root of 21501640 is about 278.0719583233.

The spelling of 21501640 in words is "twenty-one million, five hundred one thousand, six hundred forty".