77981 has 4 divisors (see below), whose sum is σ = 80700. Its totient is φ = 75264.

The previous prime is 77977. The next prime is 77983. The reversal of 77981 is 18977.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18977 = 7 ⋅2711.

It can be written as a sum of positive squares in 2 ways, for example, as 17956 + 60025 = 134^2 + 245^2 .

It is a cyclic number.

It is not a de Polignac number, because 77981 - 2² = 77977 is a prime.

It is a super-2 number, since 2×77981² = 12162072722, 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 (77983) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1316 + ... + 1373.

It is an arithmetic number, because the mean of its divisors is an integer number (20175).

2⁷⁷⁹⁸¹ is an apocalyptic number.

It is an amenable number.

77981 is a deficient number, since it is larger than the sum of its proper divisors (2719).

77981 is a wasteful number, since it uses less digits than its factorization.

77981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2718.

The product of its digits is 3528, while the sum is 32.

The square root of 77981 is about 279.2507833472. The cubic root of 77981 is about 42.7231172825.

The spelling of 77981 in words is "seventy-seven thousand, nine hundred eighty-one".