209987820 has 72 divisors (see below), whose sum is σ = 727962144. Its totient is φ = 47996928.

The previous prime is 209987807. The next prime is 209987837. The reversal of 209987820 is 28789902.

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

It is an unprimeable number.

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 23 ways as a sum of consecutive naturals, for example, 82069 + ... + 84588.

Almost surely, 2^209987820 is an apocalyptic number.

209987820 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

209987820 is an abundant number, since it is smaller than the sum of its proper divisors (517974324).

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

209987820 is a wasteful number, since it uses less digits than its factorization.

209987820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 166679 (or 166674 counting only the distinct ones).

The product of its (nonzero) digits is 145152, while the sum is 45.

The square root of 209987820 is about 14490.9564901700. The cubic root of 209987820 is about 594.3807034717.

The spelling of 209987820 in words is "two hundred nine million, nine hundred eighty-seven thousand, eight hundred twenty".