1681961891 has 2 divisors, whose sum is σ = 1681961892. Its totient is φ = 1681961890.

The previous prime is 1681961863. The next prime is 1681961969. The reversal of 1681961891 is 1981691861.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1681961891 is a prime.

1681961891 is a strobogrammatic number because it is the same when read upside-down.

It is not a weakly prime, because it can be changed into another prime (1681961851) 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, 840980945 + 840980946.

It is an arithmetic number, because the mean of its divisors is an integer number (840980946).

Almost surely, 2^1681961891 is an apocalyptic number.

1681961891 is a deficient number, since it is larger than the sum of its proper divisors (1).

1681961891 is an equidigital number, since it uses as much as digits as its factorization.

1681961891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 186624, while the sum is 50.

The square root of 1681961891 is about 41011.7287004584. The cubic root of 1681961891 is about 1189.2469616078.

The spelling of 1681961891 in words is "one billion, six hundred eighty-one million, nine hundred sixty-one thousand, eight hundred ninety-one".