138617821 has 2 divisors, whose sum is σ = 138617822. Its totient is φ = 138617820.

The previous prime is 138617819. The next prime is 138617827. The reversal of 138617821 is 128716831.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 134815321 + 3802500 = 11611^2 + 1950^2 .

It is a cyclic number.

It is not a de Polignac number, because 138617821 - 2¹ = 138617819 is a prime.

Together with 138617819, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (138617827) 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, 69308910 + 69308911.

It is an arithmetic number, because the mean of its divisors is an integer number (69308911).

Almost surely, 2^138617821 is an apocalyptic number.

It is an amenable number.

138617821 is a deficient number, since it is larger than the sum of its proper divisors (1).

138617821 is an equidigital number, since it uses as much as digits as its factorization.

138617821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 16128, while the sum is 37.

The square root of 138617821 is about 11773.6069664313. The cubic root of 138617821 is about 517.5349565253.

It can be divided in two parts, 1386 and 17821, that multiplied together give a triangular number (24699906 = T₇₀₂₈).

The spelling of 138617821 in words is "one hundred thirty-eight million, six hundred seventeen thousand, eight hundred twenty-one".