1640666 has 4 divisors (see below), whose sum is σ = 2461002. Its totient is φ = 820332.

The previous prime is 1640663. The next prime is 1640677. The reversal of 1640666 is 6660461.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 6660461 = 167 ⋅39883.

It can be written as a sum of positive squares in only one way, i.e., 1274641 + 366025 = 1129^2 + 605^2 .

It is not an unprimeable number, because it can be changed into a prime (1640663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410165 + ... + 410168.

2^1640666 is an apocalyptic number.

1640666 is a deficient number, since it is larger than the sum of its proper divisors (820336).

1640666 is an equidigital number, since it uses as much as digits as its factorization.

1640666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 820335.

The product of its (nonzero) digits is 5184, while the sum is 29.

The square root of 1640666 is about 1280.8848504062. The cubic root of 1640666 is about 117.9433319782.

The spelling of 1640666 in words is "one million, six hundred forty thousand, six hundred sixty-six".