231213721 has 2 divisors, whose sum is σ = 231213722. Its totient is φ = 231213720.

The previous prime is 231213691. The next prime is 231213737. The reversal of 231213721 is 127312132.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 195692121 + 35521600 = 13989^2 + 5960^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-231213721 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 231213692 and 231213701.

It is not a weakly prime, because it can be changed into another prime (231213751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 115606860 + 115606861.

It is an arithmetic number, because the mean of its divisors is an integer number (115606861).

Almost surely, 2^231213721 is an apocalyptic number.

It is an amenable number.

231213721 is a deficient number, since it is larger than the sum of its proper divisors (1).

231213721 is an equidigital number, since it uses as much as digits as its factorization.

231213721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 504, while the sum is 22.

The square root of 231213721 is about 15205.7134327857. The cubic root of 231213721 is about 613.7684133002.

Adding to 231213721 its reverse (127312132), we get a palindrome (358525853).

The spelling of 231213721 in words is "two hundred thirty-one million, two hundred thirteen thousand, seven hundred twenty-one".