261221663785 has 4 divisors (see below), whose sum is σ = 313465996548. Its totient is φ = 208977331024.

The previous prime is 261221663783. The next prime is 261221663803. The reversal of 261221663785 is 587366122162.

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 139439509056 + 121782154729 = 373416^2 + 348973^2 .

It is a cyclic number.

It is not a de Polignac number, because 261221663785 - 2¹ = 261221663783 is a prime.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (261221663783) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26122166374 + ... + 26122166383.

It is an arithmetic number, because the mean of its divisors is an integer number (78366499137).

Almost surely, 2^261221663785 is an apocalyptic number.

It is an amenable number.

261221663785 is a deficient number, since it is larger than the sum of its proper divisors (52244332763).

261221663785 is an equidigital number, since it uses as much as digits as its factorization.

261221663785 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 52244332762.

The product of its digits is 1451520, while the sum is 49.

The spelling of 261221663785 in words is "two hundred sixty-one billion, two hundred twenty-one million, six hundred sixty-three thousand, seven hundred eighty-five".