21573540 has 144 divisors (see below), whose sum is σ = 71180928. Its totient is φ = 5474304.

The previous prime is 21573533. The next prime is 21573547. The reversal of 21573540 is 4537512.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21573533) and next prime (21573547).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21573547) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 111684 + ... + 111876.

It is an arithmetic number, because the mean of its divisors is an integer number (494312).

Almost surely, 2^21573540 is an apocalyptic number.

21573540 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 21573540, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35590464).

21573540 is an abundant number, since it is smaller than the sum of its proper divisors (49607388).

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

21573540 is a wasteful number, since it uses less digits than its factorization.

21573540 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 240 (or 226 counting only the distinct ones).

The product of its (nonzero) digits is 4200, while the sum is 27.

The square root of 21573540 is about 4644.7325003707. The cubic root of 21573540 is about 278.3815646235.

The spelling of 21573540 in words is "twenty-one million, five hundred seventy-three thousand, five hundred forty".