1691681 has 2 divisors, whose sum is σ = 1691682. Its totient is φ = 1691680.

The previous prime is 1691659. The next prime is 1691689. The reversal of 1691681 is 1861961.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1690000 + 1681 = 1300^2 + 41^2 .

It is an emirp because it is prime and its reverse (1861961) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1691681 is a prime.

It is a super-2 number, since 2×1691681² = 5723569211522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (1691689) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 845840 + 845841.

It is an arithmetic number, because the mean of its divisors is an integer number (845841).

2^1691681 is an apocalyptic number.

It is an amenable number.

1691681 is a deficient number, since it is larger than the sum of its proper divisors (1).

1691681 is an equidigital number, since it uses as much as digits as its factorization.

1691681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2592, while the sum is 32.

The square root of 1691681 is about 1300.6463777676. The cubic root of 1691681 is about 119.1533226021.

It can be divided in two parts, 169 and 1681, that multiplied together give a square (284089 = 533²).

The spelling of 1691681 in words is "one million, six hundred ninety-one thousand, six hundred eighty-one".