21783240 has 48 divisors (see below), whose sum is σ = 70796700. Its totient is φ = 5808768.

The previous prime is 21783233. The next prime is 21783257. The reversal of 21783240 is 4238712.

It can be written as a sum of positive squares in 2 ways, for example, as 20629764 + 1153476 = 4542^2 + 1074^2 .

It is a zygodrome in base 3.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 29895 + ... + 30614.

Almost surely, 2^21783240 is an apocalyptic number.

21783240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21783240 is an abundant number, since it is smaller than the sum of its proper divisors (49013460).

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

21783240 is a wasteful number, since it uses less digits than its factorization.

21783240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 60526 (or 60519 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

The square root of 21783240 is about 4667.2518680697. The cubic root of 21783240 is about 279.2806364189.

The spelling of 21783240 in words is "twenty-one million, seven hundred eighty-three thousand, two hundred forty".