66561291 has 16 divisors (see below), whose sum is σ = 100904320. Its totient is φ = 43341480.

The previous prime is 66561289. The next prime is 66561331. The reversal of 66561291 is 19216566.

66561291 is a `hidden beast` number, since 6 + 6 + 561 + 2 + 91 = 666.

It is not a de Polignac number, because 66561291 - 2¹ = 66561289 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66561211) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 27505 + ... + 29826.

It is an arithmetic number, because the mean of its divisors is an integer number (6306520).

Almost surely, 2^66561291 is an apocalyptic number.

66561291 is a deficient number, since it is larger than the sum of its proper divisors (34343029).

66561291 is a wasteful number, since it uses less digits than its factorization.

66561291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 57383 (or 57377 counting only the distinct ones).

The product of its digits is 19440, while the sum is 36.

The square root of 66561291 is about 8158.5103419681. The cubic root of 66561291 is about 405.2663816810.

The spelling of 66561291 in words is "sixty-six million, five hundred sixty-one thousand, two hundred ninety-one".