138642561 has 12 divisors (see below), whose sum is σ = 201370260. Its totient is φ = 91916640.

The previous prime is 138642557. The next prime is 138642583. The reversal of 138642561 is 165246831.

It is a happy number.

138642561 is a `hidden beast` number, since 1 + 3 + 8 + 642 + 5 + 6 + 1 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 21678336 + 116964225 = 4656^2 + 10815^2 .

It is not a de Polignac number, because 138642561 - 2² = 138642557 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (138642061) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 40926 + ... + 44183.

It is an arithmetic number, because the mean of its divisors is an integer number (16780855).

Almost surely, 2^138642561 is an apocalyptic number.

It is an amenable number.

138642561 is a deficient number, since it is larger than the sum of its proper divisors (62727699).

138642561 is a wasteful number, since it uses less digits than its factorization.

138642561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 85296 (or 85293 counting only the distinct ones).

The product of its digits is 34560, while the sum is 36.

The square root of 138642561 is about 11774.6575746388. The cubic root of 138642561 is about 517.5657439404.

The spelling of 138642561 in words is "one hundred thirty-eight million, six hundred forty-two thousand, five hundred sixty-one".