138649981 has 2 divisors, whose sum is σ = 138649982. Its totient is φ = 138649980.

The previous prime is 138649963. The next prime is 138649993. The reversal of 138649981 is 189946831.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 82264900 + 56385081 = 9070^2 + 7509^2 .

It is a cyclic number.

It is not a de Polignac number, because 138649981 - 2¹⁷ = 138518909 is a prime.

It is a super-2 number, since 2×138649981² = 38447634462600722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (138649921) 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, 69324990 + 69324991.

It is an arithmetic number, because the mean of its divisors is an integer number (69324991).

Almost surely, 2^138649981 is an apocalyptic number.

It is an amenable number.

138649981 is a deficient number, since it is larger than the sum of its proper divisors (1).

138649981 is an equidigital number, since it uses as much as digits as its factorization.

138649981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 373248, while the sum is 49.

The square root of 138649981 is about 11774.9726538961. The cubic root of 138649981 is about 517.5749769621.

The spelling of 138649981 in words is "one hundred thirty-eight million, six hundred forty-nine thousand, nine hundred eighty-one".