231221720 has 64 divisors (see below), whose sum is σ = 532599840. Its totient is φ = 90316800.

The previous prime is 231221719. The next prime is 231221723. The reversal of 231221720 is 27122132.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a junction number, because it is equal to n+sod(n) for n = 231221692 and 231221701.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (231221723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 470675 + ... + 471165.

Almost surely, 2^231221720 is an apocalyptic number.

231221720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 231221720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (266299920).

231221720 is an abundant number, since it is smaller than the sum of its proper divisors (301378120).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

231221720 is a wasteful number, since it uses less digits than its factorization.

231221720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 756 (or 752 counting only the distinct ones).

The product of its (nonzero) digits is 336, while the sum is 20.

The square root of 231221720 is about 15205.9764566436. The cubic root of 231221720 is about 613.7754911341.

Adding to 231221720 its reverse (27122132), we get a palindrome (258343852).

It can be divided in two parts, 23122 and 1720, that added together give a palindrome (24842).

The spelling of 231221720 in words is "two hundred thirty-one million, two hundred twenty-one thousand, seven hundred twenty".