261919661 has 4 divisors (see below), whose sum is σ = 262195452. Its totient is φ = 261643872.

The previous prime is 261919657. The next prime is 261919667. The reversal of 261919661 is 166919162.

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 184144900 + 77774761 = 13570^2 + 8819^2 .

It is a cyclic number.

It is not a de Polignac number, because 261919661 - 2² = 261919657 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261919667) 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, 136466 + ... + 138371.

It is an arithmetic number, because the mean of its divisors is an integer number (65548863).

Almost surely, 2^261919661 is an apocalyptic number.

It is an amenable number.

261919661 is a deficient number, since it is larger than the sum of its proper divisors (275791).

261919661 is an equidigital number, since it uses as much as digits as its factorization.

261919661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 275790.

The product of its digits is 34992, while the sum is 41.

The square root of 261919661 is about 16183.9321859677. The cubic root of 261919661 is about 639.8173803501.

The spelling of 261919661 in words is "two hundred sixty-one million, nine hundred nineteen thousand, six hundred sixty-one".