61721936721 has 9 divisors (see below), whose sum is σ = 89154985179. Its totient is φ = 41147460936.

The previous prime is 61721936707. The next prime is 61721936743. The reversal of 61721936721 is 12763912716.

The square root of 61721936721 is 248439.

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

61721936721 is a `hidden beast` number, since 617 + 2 + 1 + 9 + 3 + 6 + 7 + 21 = 666.

61721936721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 44916444225 + 16805492496 = 211935^2 + 129636^2 .

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 61721936721 - 2¹³ = 61721928529 is a prime.

It is a super-2 number, since 2×61721936721² (a number of 22 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (61721936921) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 703911 + ... + 786723.

Almost surely, 2^61721936721 is an apocalyptic number.

61721936721 is the 248439-th square number.

61721936721 is the 124220-th centered octagonal number.

It is an amenable number.

61721936721 is a deficient number, since it is larger than the sum of its proper divisors (27433048458).

61721936721 is an frugal number, since it uses more digits than its factorization.

61721936721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 165632 (or 82816 counting only the distinct ones).

The product of its digits is 190512, while the sum is 45.

The spelling of 61721936721 in words is "sixty-one billion, seven hundred twenty-one million, nine hundred thirty-six thousand, seven hundred twenty-one".