261797981 has 4 divisors (see below), whose sum is σ = 262381500. Its totient is φ = 261214464.

The previous prime is 261797947. The next prime is 261797989. The reversal of 261797981 is 189797162.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 189797162 = 2 ⋅94898581.

It can be written as a sum of positive squares in 2 ways, for example, as 226502500 + 35295481 = 15050^2 + 5941^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261797981 is a prime.

It is a super-2 number, since 2×261797981² = 137076365711352722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261797989) 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 3 ways as a sum of consecutive naturals, for example, 291086 + ... + 291983.

It is an arithmetic number, because the mean of its divisors is an integer number (65595375).

Almost surely, 2^261797981 is an apocalyptic number.

It is an amenable number.

261797981 is a deficient number, since it is larger than the sum of its proper divisors (583519).

261797981 is an equidigital number, since it uses as much as digits as its factorization.

261797981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 583518.

The product of its digits is 381024, while the sum is 50.

The square root of 261797981 is about 16180.1724650883. The cubic root of 261797981 is about 639.7182850299.

The spelling of 261797981 in words is "two hundred sixty-one million, seven hundred ninety-seven thousand, nine hundred eighty-one".