261637891 has 4 divisors (see below), whose sum is σ = 263394000. Its totient is φ = 259881784.

The previous prime is 261637889. The next prime is 261637921. The reversal of 261637891 is 198736162.

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 261637891 - 2¹ = 261637889 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261637591) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 877831 + ... + 878128.

It is an arithmetic number, because the mean of its divisors is an integer number (65848500).

Almost surely, 2^261637891 is an apocalyptic number.

261637891 is a deficient number, since it is larger than the sum of its proper divisors (1756109).

261637891 is a wasteful number, since it uses less digits than its factorization.

261637891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1756108.

The product of its digits is 108864, while the sum is 43.

The square root of 261637891 is about 16175.2246043138. The cubic root of 261637891 is about 639.5878620958.

The spelling of 261637891 in words is "two hundred sixty-one million, six hundred thirty-seven thousand, eight hundred ninety-one".