661640921243 has 4 divisors (see below), whose sum is σ = 665296396128. Its totient is φ = 657985446360.

The previous prime is 661640921237. The next prime is 661640921269. The reversal of 661640921243 is 342129046166.

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

It is a cyclic number.

It is not a de Polignac number, because 661640921243 - 2⁸ = 661640920987 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 661640921194 and 661640921203.

It is not an unprimeable number, because it can be changed into a prime (661640951243) 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, 1827737171 + ... + 1827737532.

It is an arithmetic number, because the mean of its divisors is an integer number (166324099032).

Almost surely, 2^661640921243 is an apocalyptic number.

661640921243 is a deficient number, since it is larger than the sum of its proper divisors (3655474885).

661640921243 is a wasteful number, since it uses less digits than its factorization.

661640921243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3655474884.

The product of its (nonzero) digits is 373248, while the sum is 44.

The spelling of 661640921243 in words is "six hundred sixty-one billion, six hundred forty million, nine hundred twenty-one thousand, two hundred forty-three".