6621721566 has 16 divisors (see below), whose sum is σ = 13246266000. Its totient is φ = 2206770048.

The previous prime is 6621721553. The next prime is 6621721607. The reversal of 6621721566 is 6651271266.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 86491 + ... + 143958.

It is an arithmetic number, because the mean of its divisors is an integer number (827891625).

Almost surely, 2^6621721566 is an apocalyptic number.

6621721566 is an abundant number, since it is smaller than the sum of its proper divisors (6624544434).

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

6621721566 is a wasteful number, since it uses less digits than its factorization.

6621721566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 235243.

The product of its digits is 181440, while the sum is 42.

The square root of 6621721566 is about 81373.9612283930. The cubic root of 6621721566 is about 1877.8330213410.

The spelling of 6621721566 in words is "six billion, six hundred twenty-one million, seven hundred twenty-one thousand, five hundred sixty-six".