21542640 has 80 divisors (see below), whose sum is σ = 76328448. Its totient is φ = 4923648.

The previous prime is 21542639. The next prime is 21542663. The reversal of 21542640 is 4624512.

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 (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21542640.

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, 4732 + ... + 8091.

Almost surely, 2^21542640 is an apocalyptic number.

21542640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21542640 is an abundant number, since it is smaller than the sum of its proper divisors (54785808).

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

21542640 is a wasteful number, since it uses less digits than its factorization.

21542640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12846 (or 12840 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 24.

The square root of 21542640 is about 4641.4049597078. The cubic root of 21542640 is about 278.2485915382.

The spelling of 21542640 in words is "twenty-one million, five hundred forty-two thousand, six hundred forty".