123139981 has 2 divisors, whose sum is σ = 123139982. Its totient is φ = 123139980.

The previous prime is 123139979. The next prime is 123139997. The reversal of 123139981 is 189931321.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 105247081 + 17892900 = 10259^2 + 4230^2 .

It is an emirp because it is prime and its reverse (189931321) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 123139981 - 2¹ = 123139979 is a prime.

It is a super-2 number, since 2×123139981² = 30326909841360722, which contains 22 as substring.

Together with 123139979, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 123139981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (123139901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 61569990 + 61569991.

It is an arithmetic number, because the mean of its divisors is an integer number (61569991).

Almost surely, 2^123139981 is an apocalyptic number.

It is an amenable number.

123139981 is a deficient number, since it is larger than the sum of its proper divisors (1).

123139981 is an equidigital number, since it uses as much as digits as its factorization.

123139981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 11664, while the sum is 37.

The square root of 123139981 is about 11096.8455427657. The cubic root of 123139981 is about 497.5075709057.

The spelling of 123139981 in words is "one hundred twenty-three million, one hundred thirty-nine thousand, nine hundred eighty-one".