1666821663 has 12 divisors (see below), whose sum is σ = 2592833880. Its totient is φ = 1025736336.

The previous prime is 1666821649. The next prime is 1666821701. The reversal of 1666821663 is 3661286661.

It is not a de Polignac number, because 1666821663 - 2⁸ = 1666821407 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1666821643) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 7123053 + ... + 7123286.

It is an arithmetic number, because the mean of its divisors is an integer number (216069490).

Almost surely, 2^1666821663 is an apocalyptic number.

1666821663 is a gapful number since it is divisible by the number (13) formed by its first and last digit.

1666821663 is a deficient number, since it is larger than the sum of its proper divisors (926012217).

1666821663 is a wasteful number, since it uses less digits than its factorization.

1666821663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14246358 (or 14246355 counting only the distinct ones).

The product of its digits is 373248, while the sum is 45.

The square root of 1666821663 is about 40826.7273118970. The cubic root of 1666821663 is about 1185.6678540521.

The spelling of 1666821663 in words is "one billion, six hundred sixty-six million, eight hundred twenty-one thousand, six hundred sixty-three".