1661681 has 8 divisors (see below), whose sum is σ = 1981824. Its totient is φ = 1362240.

The previous prime is 1661677. The next prime is 1661713. The reversal of 1661681 is 1861661.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1661681 - 2² = 1661677 is a prime.

It is a super-2 number, since 2×1661681² = 5522367491522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1661641) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5000 + ... + 5321.

It is an arithmetic number, because the mean of its divisors is an integer number (247728).

2^1661681 is an apocalyptic number.

It is an amenable number.

1661681 is a deficient number, since it is larger than the sum of its proper divisors (320143).

1661681 is a wasteful number, since it uses less digits than its factorization.

1661681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10351.

The product of its digits is 1728, while the sum is 29.

The square root of 1661681 is about 1289.0620621211. The cubic root of 1661681 is about 118.4447688398. Note that the first 3 decimals are identical.

The spelling of 1661681 in words is "one million, six hundred sixty-one thousand, six hundred eighty-one".