66561555 has 16 divisors (see below), whose sum is σ = 107207424. Its totient is φ = 35263200.

The previous prime is 66561527. The next prime is 66561569. The reversal of 66561555 is 55516566.

It is a de Polignac number, because none of the positive numbers 2^k-66561555 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12429 + ... + 16958.

It is an arithmetic number, because the mean of its divisors is an integer number (6700464).

Almost surely, 2^66561555 is an apocalyptic number.

66561555 is a deficient number, since it is larger than the sum of its proper divisors (40645869).

66561555 is a wasteful number, since it uses less digits than its factorization.

66561555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 29546.

The product of its digits is 135000, while the sum is 39.

The square root of 66561555 is about 8158.5265213763. The cubic root of 66561555 is about 405.2669174788.

The spelling of 66561555 in words is "sixty-six million, five hundred sixty-one thousand, five hundred fifty-five".