1661729 has 4 divisors (see below), whose sum is σ = 1719060. Its totient is φ = 1604400.

The previous prime is 1661713. The next prime is 1661731. The reversal of 1661729 is 9271661.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 555025 + 1106704 = 745^2 + 1052^2 .

It is a cyclic number.

It is not a de Polignac number, because 1661729 - 2⁴ = 1661713 is a prime.

It is a super-4 number, since 4×1661729⁴ (a number of 26 digits) contains 4444 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 1661695 and 1661704.

It is not an unprimeable number, because it can be changed into a prime (1661789) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 28622 + ... + 28679.

It is an arithmetic number, because the mean of its divisors is an integer number (429765).

2^1661729 is an apocalyptic number.

It is an amenable number.

1661729 is a deficient number, since it is larger than the sum of its proper divisors (57331).

1661729 is an equidigital number, since it uses as much as digits as its factorization.

1661729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57330.

The product of its digits is 4536, while the sum is 32.

The square root of 1661729 is about 1289.0806801748. The cubic root of 1661729 is about 118.4459093102.

The spelling of 1661729 in words is "one million, six hundred sixty-one thousand, seven hundred twenty-nine".