661055521 has 9 divisors (see below), whose sum is σ = 769192371. Its totient is φ = 566464752.

The previous prime is 661055503. The next prime is 661055531. The reversal of 661055521 is 125550166.

The square root of 661055521 is 25711.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 42837025 + 618218496 = 6545^2 + 24864^2 .

It is not a de Polignac number, because 661055521 - 2¹¹ = 661053473 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661055531) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 178141 + ... + 181813.

It is an arithmetic number, because the mean of its divisors is an integer number (85465819).

Almost surely, 2^661055521 is an apocalyptic number.

661055521 is the 25711-st square number.

661055521 is the 12856-th centered octagonal number.

It is an amenable number.

661055521 is a deficient number, since it is larger than the sum of its proper divisors (108136850).

661055521 is an frugal number, since it uses more digits than its factorization.

661055521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7360 (or 3680 counting only the distinct ones).

The product of its (nonzero) digits is 9000, while the sum is 31.

The cubic root of 661055521 is about 871.1226626220.

The spelling of 661055521 in words is "six hundred sixty-one million, fifty-five thousand, five hundred twenty-one".