261918761 has 4 divisors (see below), whose sum is σ = 282066372. Its totient is φ = 241771152.

The previous prime is 261918703. The next prime is 261918791. The reversal of 261918761 is 167819162.

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

It can be written as a sum of positive squares in 2 ways, for example, as 118374400 + 143544361 = 10880^2 + 11981^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261918761 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261918791) 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, 10073786 + ... + 10073811.

It is an arithmetic number, because the mean of its divisors is an integer number (70516593).

Almost surely, 2^261918761 is an apocalyptic number.

It is an amenable number.

261918761 is a deficient number, since it is larger than the sum of its proper divisors (20147611).

261918761 is a wasteful number, since it uses less digits than its factorization.

261918761 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20147610.

The product of its digits is 36288, while the sum is 41.

The square root of 261918761 is about 16183.9043805875. The cubic root of 261918761 is about 639.8166475092.

The spelling of 261918761 in words is "two hundred sixty-one million, nine hundred eighteen thousand, seven hundred sixty-one".