1666595721 has 32 divisors (see below), whose sum is σ = 2601364480. Its totient is φ = 929434176.

The previous prime is 1666595713. The next prime is 1666595729. The reversal of 1666595721 is 1275956661.

It is an interprime number because it is at equal distance from previous prime (1666595713) and next prime (1666595729).

It is not a de Polignac number, because 1666595721 - 2³ = 1666595713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1666595729) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 147930 + ... + 158796.

It is an arithmetic number, because the mean of its divisors is an integer number (81292640).

Almost surely, 2^1666595721 is an apocalyptic number.

It is an amenable number.

1666595721 is a deficient number, since it is larger than the sum of its proper divisors (934768759).

1666595721 is a wasteful number, since it uses less digits than its factorization.

1666595721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11053.

The product of its digits is 680400, while the sum is 48.

The square root of 1666595721 is about 40823.9601337254. The cubic root of 1666595721 is about 1185.6142781802.

The spelling of 1666595721 in words is "one billion, six hundred sixty-six million, five hundred ninety-five thousand, seven hundred twenty-one".