209397981 has 32 divisors (see below), whose sum is σ = 308051968. Its totient is φ = 125737920.

The previous prime is 209397967. The next prime is 209398001. The reversal of 209397981 is 189793902.

It is not a de Polignac number, because 209397981 - 2⁹ = 209397469 is a prime.

It is a super-2 number, since 2×209397981² = 87695028893752722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 209397981.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (209397941) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 331536 + ... + 332166.

It is an arithmetic number, because the mean of its divisors is an integer number (9626624).

Almost surely, 2^209397981 is an apocalyptic number.

It is an amenable number.

209397981 is a deficient number, since it is larger than the sum of its proper divisors (98653987).

209397981 is a wasteful number, since it uses less digits than its factorization.

209397981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 841.

The product of its (nonzero) digits is 244944, while the sum is 48.

The square root of 209397981 is about 14470.5902091103. The cubic root of 209397981 is about 593.8236589540.

It can be divided in two parts, 20939 and 7981, that added together give a triangular number (28920 = T₂₄₀).

The spelling of 209397981 in words is "two hundred nine million, three hundred ninety-seven thousand, nine hundred eighty-one".