138391661 has 2 divisors, whose sum is σ = 138391662. Its totient is φ = 138391660.

The previous prime is 138391633. The next prime is 138391681. The reversal of 138391661 is 166193831.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 124657225 + 13734436 = 11165^2 + 3706^2 .

It is an emirp because it is prime and its reverse (166193831) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 138391661 - 2¹⁸ = 138129517 is a prime.

It is a super-3 number, since 3×138391661³ (a number of 25 digits) contains 333 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (138391601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 69195830 + 69195831.

It is an arithmetic number, because the mean of its divisors is an integer number (69195831).

Almost surely, 2^138391661 is an apocalyptic number.

It is an amenable number.

138391661 is a deficient number, since it is larger than the sum of its proper divisors (1).

138391661 is an equidigital number, since it uses as much as digits as its factorization.

138391661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23328, while the sum is 38.

The square root of 138391661 is about 11763.9985124107. The cubic root of 138391661 is about 517.2533443020.

The spelling of 138391661 in words is "one hundred thirty-eight million, three hundred ninety-one thousand, six hundred sixty-one".