138565781 has 2 divisors, whose sum is σ = 138565782. Its totient is φ = 138565780.

The previous prime is 138565769. The next prime is 138565787. The reversal of 138565781 is 187565831.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 93219025 + 45346756 = 9655^2 + 6734^2 .

It is an emirp because it is prime and its reverse (187565831) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 138565781 - 2¹⁸ = 138303637 is a prime.

It is a super-2 number, since 2×138565781² = 38400951328279922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (138565787) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 69282890 + 69282891.

It is an arithmetic number, because the mean of its divisors is an integer number (69282891).

Almost surely, 2^138565781 is an apocalyptic number.

It is an amenable number.

138565781 is a deficient number, since it is larger than the sum of its proper divisors (1).

138565781 is an equidigital number, since it uses as much as digits as its factorization.

138565781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 201600, while the sum is 44.

The square root of 138565781 is about 11771.3967310596. The cubic root of 138565781 is about 517.4701839730.

Subtracting 138565781 from its reverse (187565831), we obtain a triangular number (49000050 = T₉₈₉₉).

The spelling of 138565781 in words is "one hundred thirty-eight million, five hundred sixty-five thousand, seven hundred eighty-one".