661974881 has 4 divisors (see below), whose sum is σ = 679866132. Its totient is φ = 644083632.

The previous prime is 661974869. The next prime is 661974913. The reversal of 661974881 is 188479166.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 188479166 = 2 ⋅94239583.

It can be written as a sum of positive squares in 2 ways, for example, as 544989025 + 116985856 = 23345^2 + 10816^2 .

It is a cyclic number.

It is not a de Polignac number, because 661974881 - 2¹⁰ = 661973857 is a prime.

It is a super-2 number, since 2×661974881² = 876421486149928322, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (661974811) 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, 8945570 + ... + 8945643.

It is an arithmetic number, because the mean of its divisors is an integer number (169966533).

Almost surely, 2^661974881 is an apocalyptic number.

It is an amenable number.

661974881 is a deficient number, since it is larger than the sum of its proper divisors (17891251).

661974881 is a wasteful number, since it uses less digits than its factorization.

661974881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17891250.

The product of its digits is 580608, while the sum is 50.

The square root of 661974881 is about 25728.8725170770. The cubic root of 661974881 is about 871.5263122001.

The spelling of 661974881 in words is "six hundred sixty-one million, nine hundred seventy-four thousand, eight hundred eighty-one".