1231520021 has 2 divisors, whose sum is σ = 1231520022. Its totient is φ = 1231520020.

The previous prime is 1231520009. The next prime is 1231520071. The reversal of 1231520021 is 1200251321.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 616975921 + 614544100 = 24839^2 + 24790^2 .

It is an emirp because it is prime and its reverse (1200251321) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1231520021 - 2¹⁰ = 1231518997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1231520071) 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 as a sum of consecutive naturals, namely, 615760010 + 615760011.

It is an arithmetic number, because the mean of its divisors is an integer number (615760011).

Almost surely, 2^1231520021 is an apocalyptic number.

It is an amenable number.

1231520021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1231520021 is an equidigital number, since it uses as much as digits as its factorization.

1231520021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 1231520021 is about 35093.0195480526. The cubic root of 1231520021 is about 1071.8824466057.

Adding to 1231520021 its reverse (1200251321), we get a palindrome (2431771342).

The spelling of 1231520021 in words is "one billion, two hundred thirty-one million, five hundred twenty thousand, twenty-one".