6521661378 has 40 divisors (see below), whose sum is σ = 14636740800. Its totient is φ = 2170407960.

The previous prime is 6521661359. The next prime is 6521661389. The reversal of 6521661378 is 8731661256.

6521661378 is a `hidden beast` number, since 6 + 5 + 21 + 6 + 613 + 7 + 8 = 666.

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 70323 + ... + 134121.

It is an arithmetic number, because the mean of its divisors is an integer number (365918520).

Almost surely, 2^6521661378 is an apocalyptic number.

6521661378 is an abundant number, since it is smaller than the sum of its proper divisors (8115079422).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

6521661378 is a wasteful number, since it uses less digits than its factorization.

6521661378 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 64444 (or 64435 counting only the distinct ones).

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

The square root of 6521661378 is about 80756.8039114971. The cubic root of 6521661378 is about 1868.3263909235.

The spelling of 6521661378 in words is "six billion, five hundred twenty-one million, six hundred sixty-one thousand, three hundred seventy-eight".