123721921 has 4 divisors (see below), whose sum is σ = 124125232. Its totient is φ = 123318612.

The previous prime is 123721891. The next prime is 123721931. The reversal of 123721921 is 129127321.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 129127321 = 1867 ⋅69163.

It is a cyclic number.

It is not a de Polignac number, because 123721921 - 2⁵ = 123721889 is a prime.

It is a super-2 number, since 2×123721921² = 30614227471860482, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 123721921.

It is not an unprimeable number, because it can be changed into a prime (123721931) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 201195 + ... + 201808.

It is an arithmetic number, because the mean of its divisors is an integer number (31031308).

Almost surely, 2^123721921 is an apocalyptic number.

It is an amenable number.

123721921 is a deficient number, since it is larger than the sum of its proper divisors (403311).

123721921 is an equidigital number, since it uses as much as digits as its factorization.

123721921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 403310.

The product of its digits is 1512, while the sum is 28.

The square root of 123721921 is about 11123.0356018490. The cubic root of 123721921 is about 498.2900534989.

The spelling of 123721921 in words is "one hundred twenty-three million, seven hundred twenty-one thousand, nine hundred twenty-one".