66561415 has 4 divisors (see below), whose sum is σ = 79873704. Its totient is φ = 53249128.

The previous prime is 66561413. The next prime is 66561437. The reversal of 66561415 is 51416566.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 51416566 = 2 ⋅25708283.

It is a cyclic number.

It is not a de Polignac number, because 66561415 - 2¹ = 66561413 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66561413) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6656137 + ... + 6656146.

It is an arithmetic number, because the mean of its divisors is an integer number (19968426).

Almost surely, 2^66561415 is an apocalyptic number.

66561415 is a deficient number, since it is larger than the sum of its proper divisors (13312289).

66561415 is a wasteful number, since it uses less digits than its factorization.

66561415 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13312288.

The product of its digits is 21600, while the sum is 34.

The square root of 66561415 is about 8158.5179413911. The cubic root of 66561415 is about 405.2666333438.

The spelling of 66561415 in words is "sixty-six million, five hundred sixty-one thousand, four hundred fifteen".