66904721 has 4 divisors (see below), whose sum is σ = 72051252. Its totient is φ = 61758192.

The previous prime is 66904703. The next prime is 66904729. The reversal of 66904721 is 12740966.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 19018321 + 47886400 = 4361^2 + 6920^2 .

It is a cyclic number.

It is not a de Polignac number, because 66904721 - 2⁶ = 66904657 is a prime.

It is not an unprimeable number, because it can be changed into a prime (66904729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2573246 + ... + 2573271.

It is an arithmetic number, because the mean of its divisors is an integer number (18012813).

Almost surely, 2^66904721 is an apocalyptic number.

It is an amenable number.

66904721 is a deficient number, since it is larger than the sum of its proper divisors (5146531).

66904721 is a wasteful number, since it uses less digits than its factorization.

66904721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5146530.

The product of its (nonzero) digits is 18144, while the sum is 35.

The square root of 66904721 is about 8179.5306100045. The cubic root of 66904721 is about 405.9621912263.

It can be divided in two parts, 6690 and 4721, that added together give a palindrome (11411).

The spelling of 66904721 in words is "sixty-six million, nine hundred four thousand, seven hundred twenty-one".