21654640 has 40 divisors (see below), whose sum is σ = 57540960. Its totient is φ = 7424256.

The previous prime is 21654637. The next prime is 21654649. The reversal of 21654640 is 4645612.

It is a tau number, because it is divible by the number of its divisors (40).

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

It is a junction number, because it is equal to n+sod(n) for n = 21654599 and 21654608.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21654649) 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 7 ways as a sum of consecutive naturals, for example, 18775 + ... + 19894.

It is an arithmetic number, because the mean of its divisors is an integer number (1438524).

Almost surely, 2^21654640 is an apocalyptic number.

21654640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21654640 is an abundant number, since it is smaller than the sum of its proper divisors (35886320).

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

21654640 is a wasteful number, since it uses less digits than its factorization.

21654640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 38689 (or 38683 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 28.

The square root of 21654640 is about 4653.4546307018. The cubic root of 21654640 is about 278.7299622964.

Subtracting from 21654640 its reverse (4645612), we obtain a triangular number (17009028 = T₅₈₃₂).

The spelling of 21654640 in words is "twenty-one million, six hundred fifty-four thousand, six hundred forty".