66516781 has 4 divisors (see below), whose sum is σ = 67318272. Its totient is φ = 65715292.

The previous prime is 66516763. The next prime is 66516799. The reversal of 66516781 is 18761566.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is an interprime number because it is at equal distance from previous prime (66516763) and next prime (66516799).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66516781 is a prime.

It is a super-2 number, since 2×66516781² = 8848964309203922, 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 (66516721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 400621 + ... + 400786.

It is an arithmetic number, because the mean of its divisors is an integer number (16829568).

Almost surely, 2^66516781 is an apocalyptic number.

It is an amenable number.

66516781 is a deficient number, since it is larger than the sum of its proper divisors (801491).

66516781 is an equidigital number, since it uses as much as digits as its factorization.

66516781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 801490.

The product of its digits is 60480, while the sum is 40.

The square root of 66516781 is about 8155.7820593736. The cubic root of 66516781 is about 405.1760267180.

The spelling of 66516781 in words is "sixty-six million, five hundred sixteen thousand, seven hundred eighty-one".