6686157521 has 4 divisors (see below), whose sum is σ = 6687979572. Its totient is φ = 6684335472.

The previous prime is 6686157509. The next prime is 6686157547. The reversal of 6686157521 is 1257516866.

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

It can be written as a sum of positive squares in 2 ways, for example, as 2804867521 + 3881290000 = 52961^2 + 62300^2 .

It is a cyclic number.

It is not a de Polignac number, because 6686157521 - 2²² = 6681963217 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6686157421) 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, 905510 + ... + 912863.

It is an arithmetic number, because the mean of its divisors is an integer number (1671994893).

Almost surely, 2^6686157521 is an apocalyptic number.

It is an amenable number.

6686157521 is a deficient number, since it is larger than the sum of its proper divisors (1822051).

6686157521 is a wasteful number, since it uses less digits than its factorization.

6686157521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1822050.

The product of its digits is 604800, while the sum is 47.

The square root of 6686157521 is about 81768.9276008925. The cubic root of 6686157521 is about 1883.9044328089.

The spelling of 6686157521 in words is "six billion, six hundred eighty-six million, one hundred fifty-seven thousand, five hundred twenty-one".