661142891 has 4 divisors (see below), whose sum is σ = 669108552. Its totient is φ = 653177232.

The previous prime is 661142887. The next prime is 661142929. The reversal of 661142891 is 198241166.

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 661142891 - 2² = 661142887 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (661142831) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3982706 + ... + 3982871.

It is an arithmetic number, because the mean of its divisors is an integer number (167277138).

Almost surely, 2^661142891 is an apocalyptic number.

661142891 is a deficient number, since it is larger than the sum of its proper divisors (7965661).

661142891 is an equidigital number, since it uses as much as digits as its factorization.

661142891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7965660.

The product of its digits is 20736, while the sum is 38.

The square root of 661142891 is about 25712.6990220786. The cubic root of 661142891 is about 871.1610389418.

The spelling of 661142891 in words is "six hundred sixty-one million, one hundred forty-two thousand, eight hundred ninety-one".