661755763321 has 4 divisors (see below), whose sum is σ = 663843321252. Its totient is φ = 659668205392.

The previous prime is 661755763313. The next prime is 661755763327. The reversal of 661755763321 is 123367557166.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 355049139600 + 306706623721 = 595860^2 + 553811^2 .

It is a cyclic number.

It is not a de Polignac number, because 661755763321 - 2³ = 661755763313 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661755763327) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1043778490 + ... + 1043779123.

It is an arithmetic number, because the mean of its divisors is an integer number (165960830313).

Almost surely, 2^661755763321 is an apocalyptic number.

It is an amenable number.

661755763321 is a deficient number, since it is larger than the sum of its proper divisors (2087557931).

661755763321 is a wasteful number, since it uses less digits than its factorization.

661755763321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2087557930.

The product of its digits is 4762800, while the sum is 52.

The spelling of 661755763321 in words is "six hundred sixty-one billion, seven hundred fifty-five million, seven hundred sixty-three thousand, three hundred twenty-one".