138621891 has 16 divisors (see below), whose sum is σ = 197303040. Its totient is φ = 86315040.

The previous prime is 138621877. The next prime is 138621907. The reversal of 138621891 is 198126831.

It is not a de Polignac number, because 138621891 - 2¹¹ = 138619843 is a prime.

It is not an unprimeable number, because it can be changed into a prime (138621841) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13080 + ... + 21173.

It is an arithmetic number, because the mean of its divisors is an integer number (12331440).

Almost surely, 2^138621891 is an apocalyptic number.

138621891 is a deficient number, since it is larger than the sum of its proper divisors (58681149).

138621891 is a wasteful number, since it uses less digits than its factorization.

138621891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 34346.

The product of its digits is 20736, while the sum is 39.

The square root of 138621891 is about 11773.7798093900. The cubic root of 138621891 is about 517.5400216428.

It can be divided in two parts, 13862 and 1891, that added together give a triangular number (15753 = T₁₇₇).

The spelling of 138621891 in words is "one hundred thirty-eight million, six hundred twenty-one thousand, eight hundred ninety-one".