66618981 has 48 divisors (see below), whose sum is σ = 116188800. Its totient is φ = 36236160.

The previous prime is 66618977. The next prime is 66618989. The reversal of 66618981 is 18981666.

It is a happy number.

It is not a de Polignac number, because 66618981 - 2² = 66618977 is a prime.

It is a super-2 number, since 2×66618981² = 8876177258956722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66618989) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 46920 + ... + 48318.

It is an arithmetic number, because the mean of its divisors is an integer number (2420600).

Almost surely, 2^66618981 is an apocalyptic number.

It is an amenable number.

66618981 is a deficient number, since it is larger than the sum of its proper divisors (49569819).

66618981 is a wasteful number, since it uses less digits than its factorization.

66618981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1466 (or 1463 counting only the distinct ones).

The product of its digits is 124416, while the sum is 45.

The square root of 66618981 is about 8162.0451481231. The cubic root of 66618981 is about 405.3834320260.

The spelling of 66618981 in words is "sixty-six million, six hundred eighteen thousand, nine hundred eighty-one".