823951981 has 2 divisors, whose sum is σ = 823951982. Its totient is φ = 823951980.

The previous prime is 823951979. The next prime is 823951987. The reversal of 823951981 is 189159328.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 450882756 + 373069225 = 21234^2 + 19315^2 .

It is a cyclic number.

It is not a de Polignac number, because 823951981 - 2¹ = 823951979 is a prime.

It is a super-2 number, since 2×823951981² = 1357793733987648722, which contains 22 as substring.

Together with 823951979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (823951987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 411975990 + 411975991.

It is an arithmetic number, because the mean of its divisors is an integer number (411975991).

Almost surely, 2^823951981 is an apocalyptic number.

It is an amenable number.

823951981 is a deficient number, since it is larger than the sum of its proper divisors (1).

823951981 is an equidigital number, since it uses as much as digits as its factorization.

823951981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 155520, while the sum is 46.

The square root of 823951981 is about 28704.5637660634. The cubic root of 823951981 is about 937.4914179007.

The spelling of 823951981 in words is "eight hundred twenty-three million, nine hundred fifty-one thousand, nine hundred eighty-one".