12661506521 has 4 divisors (see below), whose sum is σ = 12680209572. Its totient is φ = 12642803472.

The previous prime is 12661506461. The next prime is 12661506581. The reversal of 12661506521 is 12560516621.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12560516621 = 193 ⋅65080397.

It is an interprime number because it is at equal distance from previous prime (12661506461) and next prime (12661506581).

It can be written as a sum of positive squares in 2 ways, for example, as 10286016400 + 2375490121 = 101420^2 + 48739^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-12661506521 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (12661506581) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9350510 + ... + 9351863.

It is an arithmetic number, because the mean of its divisors is an integer number (3170052393).

Almost surely, 2^12661506521 is an apocalyptic number.

It is an amenable number.

12661506521 is a deficient number, since it is larger than the sum of its proper divisors (18703051).

12661506521 is an equidigital number, since it uses as much as digits as its factorization.

12661506521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18703050.

The product of its (nonzero) digits is 21600, while the sum is 35.

The spelling of 12661506521 in words is "twelve billion, six hundred sixty-one million, five hundred six thousand, five hundred twenty-one".