138843721 has 4 divisors (see below), whose sum is σ = 142596292. Its totient is φ = 135091152.

The previous prime is 138843707. The next prime is 138843751. The reversal of 138843721 is 127348831.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 127348831 = 29 ⋅4391339.

It can be written as a sum of positive squares in 2 ways, for example, as 129140496 + 9703225 = 11364^2 + 3115^2 .

It is a cyclic number.

It is not a de Polignac number, because 138843721 - 2⁹ = 138843209 is a prime.

It is a super-2 number, since 2×138843721² = 38555157722251682, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (37), and also a Moran number because the ratio is a prime number: 3752533 = 138843721 / (1 + 3 + 8 + 8 + 4 + 3 + 7 + 2 + 1).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (138843751) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1876230 + ... + 1876303.

It is an arithmetic number, because the mean of its divisors is an integer number (35649073).

Almost surely, 2^138843721 is an apocalyptic number.

It is an amenable number.

138843721 is a deficient number, since it is larger than the sum of its proper divisors (3752571).

138843721 is an equidigital number, since it uses as much as digits as its factorization.

138843721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3752570.

The product of its digits is 32256, while the sum is 37.

The square root of 138843721 is about 11783.1965527186. The cubic root of 138843721 is about 517.8159393859.

The spelling of 138843721 in words is "one hundred thirty-eight million, eight hundred forty-three thousand, seven hundred twenty-one".