1686687781 has 2 divisors, whose sum is σ = 1686687782. Its totient is φ = 1686687780.

The previous prime is 1686687767. The next prime is 1686687797. The reversal of 1686687781 is 1877866861.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1034651556 + 652036225 = 32166^2 + 25535^2 .

It is a cyclic number.

It is not a de Polignac number, because 1686687781 - 2¹⁵ = 1686655013 is a prime.

It is a super-2 number, since 2×1686687781² = 5689831341149407922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1686687281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 843343890 + 843343891.

It is an arithmetic number, because the mean of its divisors is an integer number (843343891).

Almost surely, 2^1686687781 is an apocalyptic number.

It is an amenable number.

1686687781 is a deficient number, since it is larger than the sum of its proper divisors (1).

1686687781 is an equidigital number, since it uses as much as digits as its factorization.

1686687781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5419008, while the sum is 58.

The square root of 1686687781 is about 41069.3046081864. The cubic root of 1686687781 is about 1190.3597483530.

The spelling of 1686687781 in words is "one billion, six hundred eighty-six million, six hundred eighty-seven thousand, seven hundred eighty-one".