1666517921 has 2 divisors, whose sum is σ = 1666517922. Its totient is φ = 1666517920.

The previous prime is 1666517917. The next prime is 1666517929. The reversal of 1666517921 is 1297156661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1446737296 + 219780625 = 38036^2 + 14825^2 .

It is a cyclic number.

It is not a de Polignac number, because 1666517921 - 2² = 1666517917 is a prime.

It is not a weakly prime, because it can be changed into another prime (1666517929) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 833258960 + 833258961.

It is an arithmetic number, because the mean of its divisors is an integer number (833258961).

Almost surely, 2^1666517921 is an apocalyptic number.

It is an amenable number.

1666517921 is a deficient number, since it is larger than the sum of its proper divisors (1).

1666517921 is an equidigital number, since it uses as much as digits as its factorization.

1666517921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 136080, while the sum is 44.

The square root of 1666517921 is about 40823.0072508138. The cubic root of 1666517921 is about 1185.5958289496.

The spelling of 1666517921 in words is "one billion, six hundred sixty-six million, five hundred seventeen thousand, nine hundred twenty-one".