66415978 has 4 divisors (see below), whose sum is σ = 99623970. Its totient is φ = 33207988.

The previous prime is 66415969. The next prime is 66416017. The reversal of 66415978 is 87951466.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 87951466 = 2 ⋅43975733.

It can be written as a sum of positive squares in only one way, i.e., 66210769 + 205209 = 8137^2 + 453^2 .

It is a super-3 number, since 3×66415978³ (a number of 24 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 16603993 + ... + 16603996.

Almost surely, 2^66415978 is an apocalyptic number.

66415978 is a deficient number, since it is larger than the sum of its proper divisors (33207992).

66415978 is a wasteful number, since it uses less digits than its factorization.

66415978 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33207991.

The product of its digits is 362880, while the sum is 46.

The square root of 66415978 is about 8149.5998674782. The cubic root of 66415978 is about 404.9712482764.

The spelling of 66415978 in words is "sixty-six million, four hundred fifteen thousand, nine hundred seventy-eight".