66691951 has 4 divisors (see below), whose sum is σ = 67091472. Its totient is φ = 66292432.

The previous prime is 66691931. The next prime is 66691979. The reversal of 66691951 is 15919666.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 66691951 - 2⁹ = 66691439 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 66691898 and 66691907.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66691931) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 199510 + ... + 199843.

It is an arithmetic number, because the mean of its divisors is an integer number (16772868).

Almost surely, 2^66691951 is an apocalyptic number.

66691951 is a deficient number, since it is larger than the sum of its proper divisors (399521).

66691951 is a wasteful number, since it uses less digits than its factorization.

66691951 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 399520.

The product of its digits is 87480, while the sum is 43.

The square root of 66691951 is about 8166.5140053759. The cubic root of 66691951 is about 405.5313880332.

The spelling of 66691951 in words is "sixty-six million, six hundred ninety-one thousand, nine hundred fifty-one".