661415521 has 4 divisors (see below), whose sum is σ = 712293652. Its totient is φ = 610537392.

The previous prime is 661415467. The next prime is 661415527. The reversal of 661415521 is 125514166.

661415521 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 87142225 + 574273296 = 9335^2 + 23964^2 .

It is a cyclic number.

It is not a de Polignac number, because 661415521 - 2²⁵ = 627861089 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661415527) 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, 25439046 + ... + 25439071.

It is an arithmetic number, because the mean of its divisors is an integer number (178073413).

Almost surely, 2^661415521 is an apocalyptic number.

It is an amenable number.

661415521 is a deficient number, since it is larger than the sum of its proper divisors (50878131).

661415521 is a wasteful number, since it uses less digits than its factorization.

661415521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50878130.

The product of its digits is 7200, while the sum is 31.

The square root of 661415521 is about 25717.9999416751. Note that the first 4 decimals coincide. The cubic root of 661415521 is about 871.2807669657.

Adding to 661415521 its reverse (125514166), we get a palindrome (786929687).

The spelling of 661415521 in words is "six hundred sixty-one million, four hundred fifteen thousand, five hundred twenty-one".