661465721 has 8 divisors (see below), whose sum is σ = 759125760. Its totient is φ = 564596928.

The previous prime is 661465621. The next prime is 661465771. The reversal of 661465721 is 127564166.

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

It is not a de Polignac number, because 661465721 - 2¹⁰ = 661464697 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661465771) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 196016 + ... + 199361.

It is an arithmetic number, because the mean of its divisors is an integer number (94890720).

Almost surely, 2^661465721 is an apocalyptic number.

It is an amenable number.

661465721 is a deficient number, since it is larger than the sum of its proper divisors (97660039).

661465721 is a wasteful number, since it uses less digits than its factorization.

661465721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 395623.

The product of its digits is 60480, while the sum is 38.

The square root of 661465721 is about 25718.9758932972. The cubic root of 661465721 is about 871.3028091800.

The spelling of 661465721 in words is "six hundred sixty-one million, four hundred sixty-five thousand, seven hundred twenty-one".