816577981 has 2 divisors, whose sum is σ = 816577982. Its totient is φ = 816577980.

The previous prime is 816577973. The next prime is 816578033. The reversal of 816577981 is 189775618.

It is an a-pointer prime, because the next prime (816578033) can be obtained adding 816577981 to its sum of digits (52).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 769174756 + 47403225 = 27734^2 + 6885^2 .

It is a cyclic number.

It is not a de Polignac number, because 816577981 - 2³ = 816577973 is a prime.

It is a super-2 number, since 2×816577981² = 1333599198108072722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (816577921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 408288990 + 408288991.

It is an arithmetic number, because the mean of its divisors is an integer number (408288991).

Almost surely, 2^816577981 is an apocalyptic number.

It is an amenable number.

816577981 is a deficient number, since it is larger than the sum of its proper divisors (1).

816577981 is an equidigital number, since it uses as much as digits as its factorization.

816577981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 846720, while the sum is 52.

The square root of 816577981 is about 28575.8286144077. The cubic root of 816577981 is about 934.6863240927.

The spelling of 816577981 in words is "eight hundred sixteen million, five hundred seventy-seven thousand, nine hundred eighty-one".