8381521781 has 4 divisors (see below), whose sum is σ = 8874552492. Its totient is φ = 7888491072.

The previous prime is 8381521763. The next prime is 8381521789. The reversal of 8381521781 is 1871251838.

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 3873070756 + 4508451025 = 62234^2 + 67145^2 .

It is a cyclic number.

It is not a de Polignac number, because 8381521781 - 2²⁶ = 8314412917 is a prime.

It is a super-2 number, since 2×8381521781² (a number of 21 digits) 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 (8381521789) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 246515330 + ... + 246515363.

It is an arithmetic number, because the mean of its divisors is an integer number (2218638123).

Almost surely, 2^8381521781 is an apocalyptic number.

It is an amenable number.

8381521781 is a deficient number, since it is larger than the sum of its proper divisors (493030711).

8381521781 is a wasteful number, since it uses less digits than its factorization.

8381521781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 493030710.

The product of its digits is 107520, while the sum is 44.

The square root of 8381521781 is about 91550.6514504403. The cubic root of 8381521781 is about 2031.3010483221.

The spelling of 8381521781 in words is "eight billion, three hundred eighty-one million, five hundred twenty-one thousand, seven hundred eighty-one".