66816815 has 16 divisors (see below), whose sum is σ = 86940000. Its totient is φ = 49003392.

The previous prime is 66816809. The next prime is 66816829. The reversal of 66816815 is 51861866.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 66816815 - 2¹⁸ = 66554671 is a prime.

It is a congruent number.

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, 6236 + ... + 13134.

It is an arithmetic number, because the mean of its divisors is an integer number (5433750).

Almost surely, 2^66816815 is an apocalyptic number.

66816815 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

66816815 is a deficient number, since it is larger than the sum of its proper divisors (20123185).

66816815 is a wasteful number, since it uses less digits than its factorization.

66816815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7066.

The product of its digits is 69120, while the sum is 41.

The square root of 66816815 is about 8174.1553080425. The cubic root of 66816815 is about 405.7843156207.

The spelling of 66816815 in words is "sixty-six million, eight hundred sixteen thousand, eight hundred fifteen".