9566991721 has 27 divisors (see below), whose sum is σ = 11327545989. Its totient is φ = 8056496448.

The previous prime is 9566991683. The next prime is 9566991761. The reversal of 9566991721 is 1271996659.

The square root of 9566991721 is 97811.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 2572011225 + 6994980496 = 50715^2 + 83636^2 .

It is not a de Polignac number, because 9566991721 - 2¹⁹ = 9566467433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (9566991761) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 60936175 + ... + 60936331.

Almost surely, 2^9566991721 is an apocalyptic number.

9566991721 is the 97811-st square number.

9566991721 is the 48906-th centered octagonal number.

It is an amenable number.

9566991721 is a deficient number, since it is larger than the sum of its proper divisors (1760554268).

9566991721 is an frugal number, since it uses more digits than its factorization.

9566991721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 506 (or 253 counting only the distinct ones).

The product of its digits is 1837080, while the sum is 55.

The cubic root of 9566991721 is about 2122.8784710427.

It can be divided in two parts, 956699 and 1721, that added together give a triangular number (958420 = T₁₃₈₄).

The spelling of 9566991721 in words is "nine billion, five hundred sixty-six million, nine hundred ninety-one thousand, seven hundred twenty-one".