6661561 has 9 divisors (see below), whose sum is σ = 6977581. Its totient is φ = 6359584.

The previous prime is 6661553. The next prime is 6661583. The reversal of 6661561 is 1651666.

The square root of 6661561 is 2581.

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

It can be written as a sum of positive squares in 4 ways, for example, as 609961 + 6051600 = 781^2 + 2460^2 .

It is not a de Polignac number, because 6661561 - 2³ = 6661553 is a prime.

It is a Duffinian number.

6661561 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (6661511) 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 in 8 ways as a sum of consecutive naturals, for example, 74805 + ... + 74893.

Almost surely, 2^6661561 is an apocalyptic number.

6661561 is the 2581-st square number.

6661561 is the 1291-st centered octagonal number.

It is an amenable number.

6661561 is a deficient number, since it is larger than the sum of its proper divisors (316020).

6661561 is an frugal number, since it uses more digits than its factorization.

6661561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 236 (or 118 counting only the distinct ones).

The product of its digits is 6480, while the sum is 31.

The cubic root of 6661561 is about 188.1591473428.

The spelling of 6661561 in words is "six million, six hundred sixty-one thousand, five hundred sixty-one".