1605215666 has 4 divisors (see below), whose sum is σ = 2407823502. Its totient is φ = 802607832.

The previous prime is 1605215663. The next prime is 1605215669. The reversal of 1605215666 is 6665125061.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 6665125061 = 7 ⋅952160723.

It is an interprime number because it is at equal distance from previous prime (1605215663) and next prime (1605215669).

It can be written as a sum of positive squares in only one way, i.e., 1378562641 + 226653025 = 37129^2 + 15055^2 .

It is not an unprimeable number, because it can be changed into a prime (1605215663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 401303915 + ... + 401303918.

Almost surely, 2^1605215666 is an apocalyptic number.

1605215666 is a deficient number, since it is larger than the sum of its proper divisors (802607836).

1605215666 is an equidigital number, since it uses as much as digits as its factorization.

1605215666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 802607835.

The product of its (nonzero) digits is 64800, while the sum is 38.

The square root of 1605215666 is about 40065.1427802273. The cubic root of 1605215666 is about 1170.8766084918.

The spelling of 1605215666 in words is "one billion, six hundred five million, two hundred fifteen thousand, six hundred sixty-six".