138391681 has 2 divisors, whose sum is σ = 138391682. Its totient is φ = 138391680.

The previous prime is 138391661. The next prime is 138391703. The reversal of 138391681 is 186193831.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 98903025 + 39488656 = 9945^2 + 6284^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-138391681 is a prime.

It is a super-2 number, since 2×138391681² = 38304514740011522, which contains 22 as substring.

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, 69195840 + 69195841.

It is an arithmetic number, because the mean of its divisors is an integer number (69195841).

Almost surely, 2^138391681 is an apocalyptic number.

It is an amenable number.

138391681 is a deficient number, since it is larger than the sum of its proper divisors (1).

138391681 is an equidigital number, since it uses as much as digits as its factorization.

138391681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 31104, while the sum is 40.

The square root of 138391681 is about 11763.9993624617. Note that the first 3 decimals coincide. The cubic root of 138391681 is about 517.2533692193.

The spelling of 138391681 in words is "one hundred thirty-eight million, three hundred ninety-one thousand, six hundred eighty-one".