138816221 has 2 divisors, whose sum is σ = 138816222. Its totient is φ = 138816220.

The previous prime is 138816173. The next prime is 138816257. The reversal of 138816221 is 122618831.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 127351225 + 11464996 = 11285^2 + 3386^2 .

It is an emirp because it is prime and its reverse (122618831) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 138816221 - 2¹⁸ = 138554077 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (138816281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 69408110 + 69408111.

It is an arithmetic number, because the mean of its divisors is an integer number (69408111).

Almost surely, 2^138816221 is an apocalyptic number.

It is an amenable number.

138816221 is a deficient number, since it is larger than the sum of its proper divisors (1).

138816221 is an equidigital number, since it uses as much as digits as its factorization.

138816221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4608, while the sum is 32.

The square root of 138816221 is about 11782.0295789817. The cubic root of 138816221 is about 517.7817501587.

It can be divided in two parts, 13881 and 6221, that added together give a palindrome (20102).

The spelling of 138816221 in words is "one hundred thirty-eight million, eight hundred sixteen thousand, two hundred twenty-one".