816315781 has 4 divisors (see below), whose sum is σ = 836225964. Its totient is φ = 796405600.

The previous prime is 816315779. The next prime is 816315803. The reversal of 816315781 is 187513618.

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 169885156 + 646430625 = 13034^2 + 25425^2 .

It is a cyclic number.

It is not a de Polignac number, because 816315781 - 2¹ = 816315779 is a prime.

It is a super-2 number, since 2×816315781² = 1332742908619279922, 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 (816315761) 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, 9955030 + ... + 9955111.

It is an arithmetic number, because the mean of its divisors is an integer number (209056491).

Almost surely, 2^816315781 is an apocalyptic number.

It is an amenable number.

816315781 is a deficient number, since it is larger than the sum of its proper divisors (19910183).

816315781 is a wasteful number, since it uses less digits than its factorization.

816315781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19910182.

The product of its digits is 40320, while the sum is 40.

The square root of 816315781 is about 28571.2404525950. The cubic root of 816315781 is about 934.5862720072.

The spelling of 816315781 in words is "eight hundred sixteen million, three hundred fifteen thousand, seven hundred eighty-one".