661721549 has 8 divisors (see below), whose sum is σ = 700870968. Its totient is φ = 622597120.

The previous prime is 661721527. The next prime is 661721563. The reversal of 661721549 is 945127166.

661721549 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 4 ways, for example, as 203975524 + 457746025 = 14282^2 + 21395^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 661721549 - 2¹² = 661717453 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661721519) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 102629 + ... + 108885.

It is an arithmetic number, because the mean of its divisors is an integer number (87608871).

Almost surely, 2^661721549 is an apocalyptic number.

It is an amenable number.

661721549 is a deficient number, since it is larger than the sum of its proper divisors (39149419).

661721549 is a wasteful number, since it uses less digits than its factorization.

661721549 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12495.

The product of its digits is 90720, while the sum is 41.

The square root of 661721549 is about 25723.9489386836. The cubic root of 661721549 is about 871.4151228482.

The spelling of 661721549 in words is "six hundred sixty-one million, seven hundred twenty-one thousand, five hundred forty-nine".