66521591 has 8 divisors (see below), whose sum is σ = 68325120. Its totient is φ = 64734328.

The previous prime is 66521573. The next prime is 66521599. The reversal of 66521591 is 19512566.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 66521591 - 2¹⁸ = 66259447 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 (66521599) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4460 + ... + 12366.

It is an arithmetic number, because the mean of its divisors is an integer number (8540640).

Almost surely, 2^66521591 is an apocalyptic number.

66521591 is a deficient number, since it is larger than the sum of its proper divisors (1803529).

66521591 is a wasteful number, since it uses less digits than its factorization.

66521591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8133.

The product of its digits is 16200, while the sum is 35.

The square root of 66521591 is about 8156.0769368613. The cubic root of 66521591 is about 405.1857929238.

The spelling of 66521591 in words is "sixty-six million, five hundred twenty-one thousand, five hundred ninety-one".