1666721518 has 48 divisors (see below), whose sum is σ = 3148397280. Its totient is φ = 647760960.

The previous prime is 1666721513. The next prime is 1666721533. The reversal of 1666721518 is 8151276661.

It is a Smith number, since the sum of its digits (43) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1666721513) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 861280 + ... + 863212.

It is an arithmetic number, because the mean of its divisors is an integer number (65591610).

Almost surely, 2^1666721518 is an apocalyptic number.

1666721518 is a deficient number, since it is larger than the sum of its proper divisors (1481675762).

1666721518 is a wasteful number, since it uses less digits than its factorization.

1666721518 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2473 (or 2462 counting only the distinct ones).

The product of its digits is 120960, while the sum is 43.

The square root of 1666721518 is about 40825.5008297510. The cubic root of 1666721518 is about 1185.6441080434.

The spelling of 1666721518 in words is "one billion, six hundred sixty-six million, seven hundred twenty-one thousand, five hundred eighteen".