1681721761 has 2 divisors, whose sum is σ = 1681721762. Its totient is φ = 1681721760.

The previous prime is 1681721707. The next prime is 1681721771. The reversal of 1681721761 is 1671271861.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1660155025 + 21566736 = 40745^2 + 4644^2 .

It is a cyclic number.

It is not a de Polignac number, because 1681721761 - 2¹³ = 1681713569 is a prime.

It is a super-2 number, since 2×1681721761² = 5656376162841882242, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1681721771) 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, 840860880 + 840860881.

It is an arithmetic number, because the mean of its divisors is an integer number (840860881).

Almost surely, 2^1681721761 is an apocalyptic number.

It is an amenable number.

1681721761 is a deficient number, since it is larger than the sum of its proper divisors (1).

1681721761 is an equidigital number, since it uses as much as digits as its factorization.

1681721761 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 28224, while the sum is 40.

The square root of 1681721761 is about 41008.8010188057. The cubic root of 1681721761 is about 1189.1903635232.

The spelling of 1681721761 in words is "one billion, six hundred eighty-one million, seven hundred twenty-one thousand, seven hundred sixty-one".