66487781 has 4 divisors (see below), whose sum is σ = 66556812. Its totient is φ = 66418752.

The previous prime is 66487763. The next prime is 66487789. The reversal of 66487781 is 18778466.

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 40119556 + 26368225 = 6334^2 + 5135^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66487781 is a prime.

It is a super-2 number, since 2×66487781² = 8841250044607922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66487789) 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, 33050 + ... + 35003.

It is an arithmetic number, because the mean of its divisors is an integer number (16639203).

Almost surely, 2^66487781 is an apocalyptic number.

It is an amenable number.

66487781 is a deficient number, since it is larger than the sum of its proper divisors (69031).

66487781 is an equidigital number, since it uses as much as digits as its factorization.

66487781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 69030.

The product of its digits is 451584, while the sum is 47.

The square root of 66487781 is about 8154.0039857729. The cubic root of 66487781 is about 405.1171352493.

The spelling of 66487781 in words is "sixty-six million, four hundred eighty-seven thousand, seven hundred eighty-one".