21640560 has 80 divisors (see below), whose sum is σ = 68927136. Its totient is φ = 5612544.

The previous prime is 21640559. The next prime is 21640561. The reversal of 21640560 is 6504612.

It is an interprime number because it is at equal distance from previous prime (21640559) and next prime (21640561).

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

It is a super-2 number, since 2×21640560² = 936627674227200, which contains 22 as substring.

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 21640560.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7662 + ... + 10098.

Almost surely, 2^21640560 is an apocalyptic number.

21640560 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 21640560, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34463568).

21640560 is an abundant number, since it is smaller than the sum of its proper divisors (47286576).

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

21640560 is a wasteful number, since it uses less digits than its factorization.

21640560 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2490 (or 2484 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21640560 is about 4651.9415301571. The cubic root of 21640560 is about 278.6695384679.

The spelling of 21640560 in words is "twenty-one million, six hundred forty thousand, five hundred sixty".