1800138721 has 16 divisors (see below), whose sum is σ = 2035376640. Its totient is φ = 1583043840.

The previous prime is 1800138719. The next prime is 1800138737. The reversal of 1800138721 is 1278310081.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 1800138721 - 2¹ = 1800138719 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1800138701) 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, 43611 + ... + 74176.

It is an arithmetic number, because the mean of its divisors is an integer number (127211040).

Almost surely, 2^1800138721 is an apocalyptic number.

It is an amenable number.

1800138721 is a deficient number, since it is larger than the sum of its proper divisors (235237919).

1800138721 is a wasteful number, since it uses less digits than its factorization.

1800138721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117864.

The product of its (nonzero) digits is 2688, while the sum is 31.

The square root of 1800138721 is about 42428.0416823591. The cubic root of 1800138721 is about 1216.4716475395.

The spelling of 1800138721 in words is "one billion, eight hundred million, one hundred thirty-eight thousand, seven hundred twenty-one".