1646681581 has 2 divisors, whose sum is σ = 1646681582. Its totient is φ = 1646681580.

The previous prime is 1646681551. The next prime is 1646681593. The reversal of 1646681581 is 1851866461.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1639440100 + 7241481 = 40490^2 + 2691^2 .

It is a cyclic number.

It is not a de Polignac number, because 1646681581 - 2²⁷ = 1512463853 is a prime.

It is a super-2 number, since 2×1646681581² = 5423120458409319122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1646681551) 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 as a sum of consecutive naturals, namely, 823340790 + 823340791.

It is an arithmetic number, because the mean of its divisors is an integer number (823340791).

Almost surely, 2^1646681581 is an apocalyptic number.

It is an amenable number.

1646681581 is a deficient number, since it is larger than the sum of its proper divisors (1).

1646681581 is an equidigital number, since it uses as much as digits as its factorization.

1646681581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 276480, while the sum is 46.

The square root of 1646681581 is about 40579.3245508104. The cubic root of 1646681581 is about 1180.8730446524.

The spelling of 1646681581 in words is "one billion, six hundred forty-six million, six hundred eighty-one thousand, five hundred eighty-one".