1231707721 has 4 divisors (see below), whose sum is σ = 1235197332. Its totient is φ = 1228218112.

The previous prime is 1231707683. The next prime is 1231707731. The reversal of 1231707721 is 1277071321.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 891858496 + 339849225 = 29864^2 + 18435^2 .

It is a cyclic number.

It is not a de Polignac number, because 1231707721 - 2⁹ = 1231707209 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1231707731) 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, 1744276 + ... + 1744981.

It is an arithmetic number, because the mean of its divisors is an integer number (308799333).

Almost surely, 2^1231707721 is an apocalyptic number.

It is an amenable number.

1231707721 is a deficient number, since it is larger than the sum of its proper divisors (3489611).

1231707721 is an equidigital number, since it uses as much as digits as its factorization.

1231707721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3489610.

The product of its (nonzero) digits is 4116, while the sum is 31.

The square root of 1231707721 is about 35095.6937671846. The cubic root of 1231707721 is about 1071.9369002108.

The spelling of 1231707721 in words is "one billion, two hundred thirty-one million, seven hundred seven thousand, seven hundred twenty-one".