1657021666 has 4 divisors (see below), whose sum is σ = 2485532502. Its totient is φ = 828510832.

The previous prime is 1657021661. The next prime is 1657021693. The reversal of 1657021666 is 6661207561.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 6661207561 = 137 ⋅48621953.

It can be written as a sum of positive squares in only one way, i.e., 1570140625 + 86881041 = 39625^2 + 9321^2 .

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (1657021661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 414255415 + ... + 414255418.

Almost surely, 2^1657021666 is an apocalyptic number.

1657021666 is a deficient number, since it is larger than the sum of its proper divisors (828510836).

1657021666 is an equidigital number, since it uses as much as digits as its factorization.

1657021666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 828510835.

The product of its (nonzero) digits is 90720, while the sum is 40.

The square root of 1657021666 is about 40706.5309993372. The cubic root of 1657021666 is about 1183.3395929224.

The spelling of 1657021666 in words is "one billion, six hundred fifty-seven million, twenty-one thousand, six hundred sixty-six".