21581560 has 192 divisors, whose sum is σ = 67032000. Its totient is φ = 6209280.

The previous prime is 21581543. The next prime is 21581561. The reversal of 21581560 is 6518512.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21581561) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1660114 + ... + 1660126.

It is an arithmetic number, because the mean of its divisors is an integer number (349125).

Almost surely, 2^21581560 is an apocalyptic number.

21581560 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 21581560, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33516000).

21581560 is an abundant number, since it is smaller than the sum of its proper divisors (45450440).

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

21581560 is a wasteful number, since it uses less digits than its factorization.

21581560 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67 (or 38 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 28.

The square root of 21581560 is about 4645.5957637315. The cubic root of 21581560 is about 278.4160566223.

It can be divided in two parts, 21 and 581560, that added together give a triangular number (581581 = T₁₀₇₈).

The spelling of 21581560 in words is "twenty-one million, five hundred eighty-one thousand, five hundred sixty".