661397944957 has 4 divisors (see below), whose sum is σ = 664286145820. Its totient is φ = 658509744096.

The previous prime is 661397944943. The next prime is 661397945023. The reversal of 661397944957 is 759449793166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 759449793166 = 2 ⋅379724896583.

It can be written as a sum of positive squares in 2 ways, for example, as 541123543321 + 120274401636 = 735611^2 + 346806^2 .

It is a cyclic number.

It is not a de Polignac number, because 661397944957 - 2³⁵ = 627038206589 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (661397944457) 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, 1444100088 + ... + 1444100545.

It is an arithmetic number, because the mean of its divisors is an integer number (166071536455).

Almost surely, 2^661397944957 is an apocalyptic number.

It is an amenable number.

661397944957 is a deficient number, since it is larger than the sum of its proper divisors (2888200863).

661397944957 is a wasteful number, since it uses less digits than its factorization.

661397944957 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2888200862.

The product of its digits is 308629440, while the sum is 70.

The spelling of 661397944957 in words is "six hundred sixty-one billion, three hundred ninety-seven million, nine hundred forty-four thousand, nine hundred fifty-seven".