21645840 has 40 divisors (see below), whose sum is σ = 67102848. Its totient is φ = 5772160.

The previous prime is 21645817. The next prime is 21645859. The reversal of 21645840 is 4854612.

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

It is a hoax number, since the sum of its digits (30) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a junction number, because it is equal to n+sod(n) for n = 21645798 and 21645807.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44856 + ... + 45335.

Almost surely, 2^21645840 is an apocalyptic number.

21645840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21645840 is an abundant number, since it is smaller than the sum of its proper divisors (45457008).

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

21645840 is a wasteful number, since it uses less digits than its factorization.

21645840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 90207 (or 90201 counting only the distinct ones).

The product of its (nonzero) digits is 7680, while the sum is 30.

The square root of 21645840 is about 4652.5090005286. The cubic root of 21645840 is about 278.6922004741.

It can be divided in two parts, 216 and 45840, that added together give a triangular number (46056 = T₃₀₃).

The spelling of 21645840 in words is "twenty-one million, six hundred forty-five thousand, eight hundred forty".