1981897165 has 4 divisors (see below), whose sum is σ = 2378276604. Its totient is φ = 1585517728.

The previous prime is 1981897153. The next prime is 1981897199. The reversal of 1981897165 is 5617981891.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 618367689 + 1363529476 = 24867^2 + 36926^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1981897165 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 198189712 + ... + 198189721.

It is an arithmetic number, because the mean of its divisors is an integer number (594569151).

Almost surely, 2^1981897165 is an apocalyptic number.

It is an amenable number.

1981897165 is a deficient number, since it is larger than the sum of its proper divisors (396379439).

1981897165 is an equidigital number, since it uses as much as digits as its factorization.

1981897165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 396379438.

The product of its digits is 1088640, while the sum is 55.

The square root of 1981897165 is about 44518.5036248974. The cubic root of 1981897165 is about 1256.1081655007.

The spelling of 1981897165 in words is "one billion, nine hundred eighty-one million, eight hundred ninety-seven thousand, one hundred sixty-five".