661343987 has 4 divisors (see below), whose sum is σ = 682677696. Its totient is φ = 640010280.

The previous prime is 661343983. The next prime is 661343989. The reversal of 661343987 is 789343166.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 789343166 = 2 ⋅394671583.

It is a cyclic number.

It is not a de Polignac number, because 661343987 - 2² = 661343983 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661343983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10666808 + ... + 10666869.

It is an arithmetic number, because the mean of its divisors is an integer number (170669424).

Almost surely, 2^661343987 is an apocalyptic number.

661343987 is a deficient number, since it is larger than the sum of its proper divisors (21333709).

661343987 is a wasteful number, since it uses less digits than its factorization.

661343987 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21333708.

The product of its digits is 653184, while the sum is 47.

The square root of 661343987 is about 25716.6091660623. The cubic root of 661343987 is about 871.2493553223.

The spelling of 661343987 in words is "six hundred sixty-one million, three hundred forty-three thousand, nine hundred eighty-seven".