3721666721 has 4 divisors (see below), whose sum is σ = 3746644500. Its totient is φ = 3696688944.

The previous prime is 3721666709. The next prime is 3721666769. The reversal of 3721666721 is 1276661273.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1276661273 = 14843 ⋅86011.

It can be written as a sum of positive squares in 2 ways, for example, as 133656721 + 3588010000 = 11561^2 + 59900^2 .

It is a cyclic number.

It is not a de Polignac number, because 3721666721 - 2¹⁴ = 3721650337 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (3721666771) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12488666 + ... + 12488963.

It is an arithmetic number, because the mean of its divisors is an integer number (936661125).

Almost surely, 2^3721666721 is an apocalyptic number.

It is an amenable number.

3721666721 is a deficient number, since it is larger than the sum of its proper divisors (24977779).

3721666721 is a wasteful number, since it uses less digits than its factorization.

3721666721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24977778.

The product of its digits is 127008, while the sum is 41.

The square root of 3721666721 is about 61005.4646814529. The cubic root of 3721666721 is about 1549.6935531528.

The spelling of 3721666721 in words is "three billion, seven hundred twenty-one million, six hundred sixty-six thousand, seven hundred twenty-one".