1691666 has 4 divisors (see below), whose sum is σ = 2537502. Its totient is φ = 845832.

The previous prime is 1691659. The next prime is 1691681. The reversal of 1691666 is 6661961.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 6661961 = 37 ⋅180053.

It can be written as a sum of positive squares in only one way, i.e., 1677025 + 14641 = 1295^2 + 121^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 422915 + ... + 422918.

2^1691666 is an apocalyptic number.

1691666 is a deficient number, since it is larger than the sum of its proper divisors (845836).

1691666 is an equidigital number, since it uses as much as digits as its factorization.

1691666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 845835.

The product of its digits is 11664, while the sum is 35.

The square root of 1691666 is about 1300.6406113912. The cubic root of 1691666 is about 119.1529704267.

The spelling of 1691666 in words is "one million, six hundred ninety-one thousand, six hundred sixty-six".