6661378521 has 20 divisors (see below), whose sum is σ = 11372513152. Its totient is φ = 3806501688.

The previous prime is 6661378517. The next prime is 6661378523. The reversal of 6661378521 is 1258731666.

It is not a de Polignac number, because 6661378521 - 2² = 6661378517 is a prime.

It is not an unprimeable number, because it can be changed into a prime (6661378523) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 5873665 + ... + 5874798.

Almost surely, 2^6661378521 is an apocalyptic number.

It is an amenable number.

6661378521 is a deficient number, since it is larger than the sum of its proper divisors (4711134631).

6661378521 is a wasteful number, since it uses less digits than its factorization.

6661378521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11748482 (or 11748473 counting only the distinct ones).

The product of its digits is 362880, while the sum is 45.

The square root of 6661378521 is about 81617.2685220475. The cubic root of 6661378521 is about 1881.5742925663.

The spelling of 6661378521 in words is "six billion, six hundred sixty-one million, three hundred seventy-eight thousand, five hundred twenty-one".