1645256666 has 4 divisors (see below), whose sum is σ = 2467885002. Its totient is φ = 822628332.

The previous prime is 1645256647. The next prime is 1645256671. The reversal of 1645256666 is 6666525461.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 6666525461 = 179 ⋅37243159.

It can be written as a sum of positive squares in only one way, i.e., 1618372441 + 26884225 = 40229^2 + 5185^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 1645256666.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 411314165 + ... + 411314168.

Almost surely, 2^1645256666 is an apocalyptic number.

1645256666 is a deficient number, since it is larger than the sum of its proper divisors (822628336).

1645256666 is an equidigital number, since it uses as much as digits as its factorization.

1645256666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 822628335.

The product of its digits is 1555200, while the sum is 47.

The square root of 1645256666 is about 40561.7635957807. The cubic root of 1645256666 is about 1180.5323333066.

The spelling of 1645256666 in words is "one billion, six hundred forty-five million, two hundred fifty-six thousand, six hundred sixty-six".