209997720 has 144 divisors (see below), whose sum is σ = 706380480. Its totient is φ = 54103680.

The previous prime is 209997707. The next prime is 209997727. The reversal of 209997720 is 27799902.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (209997727) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 345657 + ... + 346263.

It is an arithmetic number, because the mean of its divisors is an integer number (4905420).

Almost surely, 2^209997720 is an apocalyptic number.

209997720 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 209997720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (353190240).

209997720 is an abundant number, since it is smaller than the sum of its proper divisors (496382760).

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

209997720 is a wasteful number, since it uses less digits than its factorization.

209997720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 686 (or 648 counting only the distinct ones).

The product of its (nonzero) digits is 142884, while the sum is 45.

The square root of 209997720 is about 14491.2980785021. The cubic root of 209997720 is about 594.3900441349.

The spelling of 209997720 in words is "two hundred nine million, nine hundred ninety-seven thousand, seven hundred twenty".