137721721 has 4 divisors (see below), whose sum is σ = 138806272. Its totient is φ = 136637172.

The previous prime is 137721707. The next prime is 137721739. The reversal of 137721721 is 127127731.

It is a happy number.

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.

It is a cyclic number.

It is not a de Polignac number, because 137721721 - 2⁹ = 137721209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (137721751) 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, 542085 + ... + 542338.

It is an arithmetic number, because the mean of its divisors is an integer number (34701568).

Almost surely, 2^137721721 is an apocalyptic number.

It is an amenable number.

137721721 is a deficient number, since it is larger than the sum of its proper divisors (1084551).

137721721 is a wasteful number, since it uses less digits than its factorization.

137721721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1084550.

The product of its digits is 4116, while the sum is 31.

The square root of 137721721 is about 11735.4898065654. The cubic root of 137721721 is about 516.4173368389.

The spelling of 137721721 in words is "one hundred thirty-seven million, seven hundred twenty-one thousand, seven hundred twenty-one".