661131561243 has 4 divisors (see below), whose sum is σ = 881508748328. Its totient is φ = 440754374160.

The previous prime is 661131561239. The next prime is 661131561269. The reversal of 661131561243 is 342165131166.

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

It is not a de Polignac number, because 661131561243 - 2² = 661131561239 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661131561743) 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, 110188593538 + ... + 110188593543.

It is an arithmetic number, because the mean of its divisors is an integer number (220377187082).

Almost surely, 2^661131561243 is an apocalyptic number.

661131561243 is a deficient number, since it is larger than the sum of its proper divisors (220377187085).

661131561243 is a wasteful number, since it uses less digits than its factorization.

661131561243 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 220377187084.

The product of its digits is 77760, while the sum is 39.

The spelling of 661131561243 in words is "six hundred sixty-one billion, one hundred thirty-one million, five hundred sixty-one thousand, two hundred forty-three".