209508981 has 16 divisors (see below), whose sum is σ = 305363520. Its totient is φ = 126715520.

The previous prime is 209508977. The next prime is 209508983. The reversal of 209508981 is 189805902.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 209508981 - 2² = 209508977 is a prime.

It is a super-2 number, since 2×209508981² = 87788026239316722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (209508983) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 10561 + ... + 23033.

It is an arithmetic number, because the mean of its divisors is an integer number (19085220).

Almost surely, 2^209508981 is an apocalyptic number.

It is an amenable number.

209508981 is a deficient number, since it is larger than the sum of its proper divisors (95854539).

209508981 is a wasteful number, since it uses less digits than its factorization.

209508981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12996.

The product of its (nonzero) digits is 51840, while the sum is 42.

The square root of 209508981 is about 14474.4250663023. The cubic root of 209508981 is about 593.9285672923.

The spelling of 209508981 in words is "two hundred nine million, five hundred eight thousand, nine hundred eighty-one".