209705640 has 128 divisors (see below), whose sum is σ = 655983360. Its totient is φ = 53581824.

The previous prime is 209705623. The next prime is 209705653. The reversal of 209705640 is 46507902.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 323797 + ... + 324443.

It is an arithmetic number, because the mean of its divisors is an integer number (5124870).

Almost surely, 2^209705640 is an apocalyptic number.

209705640 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 209705640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (327991680).

209705640 is an abundant number, since it is smaller than the sum of its proper divisors (446277720).

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

209705640 is a wasteful number, since it uses less digits than its factorization.

209705640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 771 (or 767 counting only the distinct ones).

The product of its (nonzero) digits is 15120, while the sum is 33.

The square root of 209705640 is about 14481.2167997030. The cubic root of 209705640 is about 594.1143427354.

The spelling of 209705640 in words is "two hundred nine million, seven hundred five thousand, six hundred forty".