781981 has 4 divisors (see below), whose sum is σ = 783772. Its totient is φ = 780192.

The previous prime is 781973. The next prime is 781987. The reversal of 781981 is 189187.

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 648025 + 133956 = 805^2 + 366^2 .

It is a cyclic number.

It is not a de Polignac number, because 781981 - 2³ = 781973 is a prime.

It is a super-2 number, since 2×781981² = 1222988568722, which contains 22 as substring.

It is a Duffinian number.

781981 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (781987) 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, 241 + ... + 1273.

It is an arithmetic number, because the mean of its divisors is an integer number (195943).

2⁷⁸¹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

781981 is a deficient number, since it is larger than the sum of its proper divisors (1791).

781981 is a wasteful number, since it uses less digits than its factorization.

781981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1790.

The product of its digits is 4032, while the sum is 34.

The square root of 781981 is about 884.2968958444. The cubic root of 781981 is about 92.1295041329.

The spelling of 781981 in words is "seven hundred eighty-one thousand, nine hundred eighty-one".