816409861 has 2 divisors, whose sum is σ = 816409862. Its totient is φ = 816409860.

The previous prime is 816409859. The next prime is 816409873. The reversal of 816409861 is 168904618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 470673025 + 345736836 = 21695^2 + 18594^2 .

It is a cyclic number.

It is not a de Polignac number, because 816409861 - 2¹ = 816409859 is a prime.

It is a super-2 number, since 2×816409861² = 1333050122276078642, which contains 22 as substring.

Together with 816409859, 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 (816409661) 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, 408204930 + 408204931.

It is an arithmetic number, because the mean of its divisors is an integer number (408204931).

Almost surely, 2^816409861 is an apocalyptic number.

It is an amenable number.

816409861 is a deficient number, since it is larger than the sum of its proper divisors (1).

816409861 is an equidigital number, since it uses as much as digits as its factorization.

816409861 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 82944, while the sum is 43.

The square root of 816409861 is about 28572.8868160009. The cubic root of 816409861 is about 934.6221741670.

The spelling of 816409861 in words is "eight hundred sixteen million, four hundred nine thousand, eight hundred sixty-one".