66820815 has 64 divisors (see below), whose sum is σ = 126720000. Its totient is φ = 33312384.

The previous prime is 66820811. The next prime is 66820847. The reversal of 66820815 is 51802866.

66820815 = 187² + 188² + ... + 591².

It is a happy number.

It is not a de Polignac number, because 66820815 - 2² = 66820811 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 66820815.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66820811) 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 63 ways as a sum of consecutive naturals, for example, 279466 + ... + 279704.

It is an arithmetic number, because the mean of its divisors is an integer number (1980000).

Almost surely, 2^66820815 is an apocalyptic number.

66820815 is a deficient number, since it is larger than the sum of its proper divisors (59899185).

66820815 is a wasteful number, since it uses less digits than its factorization.

66820815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 381 (or 375 counting only the distinct ones).

The product of its (nonzero) digits is 23040, while the sum is 36.

The square root of 66820815 is about 8174.3999779800. The cubic root of 66820815 is about 405.7924129082.

The spelling of 66820815 in words is "sixty-six million, eight hundred twenty thousand, eight hundred fifteen".