21387123 has 12 divisors (see below), whose sum is σ = 31958160. Its totient is φ = 13766256.

The previous prime is 21387109. The next prime is 21387151. The reversal of 21387123 is 32178312.

It is not a de Polignac number, because 21387123 - 2⁶ = 21387059 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21387193) 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, 40711 + ... + 41232.

It is an arithmetic number, because the mean of its divisors is an integer number (2663180).

Almost surely, 2^21387123 is an apocalyptic number.

21387123 is a deficient number, since it is larger than the sum of its proper divisors (10571037).

21387123 is a wasteful number, since it uses less digits than its factorization.

21387123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81978 (or 81975 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21387123 is about 4624.6213899086. The cubic root of 21387123 is about 277.5774120528.

It can be divided in two parts, 2138 and 7123, that added together give a cube (9261 = 21³).

The spelling of 21387123 in words is "twenty-one million, three hundred eighty-seven thousand, one hundred twenty-three".