137685721 has 4 divisors (see below), whose sum is σ = 137763072. Its totient is φ = 137608372.

The previous prime is 137685697. The next prime is 137685727. The reversal of 137685721 is 127586731.

137685721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 127586731 = 31 ⋅4115701.

It is a cyclic number.

It is not a de Polignac number, because 137685721 - 2⁵ = 137685689 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (137685727) 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, 35941 + ... + 39586.

It is an arithmetic number, because the mean of its divisors is an integer number (34440768).

Almost surely, 2^137685721 is an apocalyptic number.

It is an amenable number.

137685721 is a deficient number, since it is larger than the sum of its proper divisors (77351).

137685721 is an equidigital number, since it uses as much as digits as its factorization.

137685721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 77350.

The product of its digits is 70560, while the sum is 40.

The square root of 137685721 is about 11733.9558973093. The cubic root of 137685721 is about 516.3723363260.

The spelling of 137685721 in words is "one hundred thirty-seven million, six hundred eighty-five thousand, seven hundred twenty-one".