1231542135521 has 4 divisors (see below), whose sum is σ = 1231544895252. Its totient is φ = 1231539375792.

The previous prime is 1231542135517. The next prime is 1231542135559. The reversal of 1231542135521 is 1255312451321.

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 336794515600 + 894747619921 = 580340^2 + 945911^2 .

It is a cyclic number.

It is not a de Polignac number, because 1231542135521 - 2² = 1231542135517 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1231542135581) 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, 540146 + ... + 1659771.

It is an arithmetic number, because the mean of its divisors is an integer number (307886223813).

Almost surely, 2^{1231542135521} is an apocalyptic number.

It is an amenable number.

1231542135521 is a deficient number, since it is larger than the sum of its proper divisors (2759731).

1231542135521 is an equidigital number, since it uses as much as digits as its factorization.

1231542135521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2759730.

The product of its digits is 36000, while the sum is 35.

Adding to 1231542135521 its reverse (1255312451321), we get a palindrome (2486854586842).

The spelling of 1231542135521 in words is "one trillion, two hundred thirty-one billion, five hundred forty-two million, one hundred thirty-five thousand, five hundred twenty-one".