261171604655981 has 2 divisors, whose sum is σ = 261171604655982. Its totient is φ = 261171604655980.

The previous prime is 261171604655977. The next prime is 261171604656023. The reversal of 261171604655981 is 189556406171162.

It is a happy number.

261171604655981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 205539533222500 + 55632071433481 = 14336650^2 + 7458691^2 .

It is a cyclic number.

It is not a de Polignac number, because 261171604655981 - 2² = 261171604655977 is a prime.

It is a super-2 number, since 2×261171604655981² (a number of 30 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261171604654981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130585802327990 + 130585802327991.

It is an arithmetic number, because the mean of its divisors is an integer number (130585802327991).

Almost surely, 2^{261171604655981} is an apocalyptic number.

It is an amenable number.

261171604655981 is a deficient number, since it is larger than the sum of its proper divisors (1).

261171604655981 is an equidigital number, since it uses as much as digits as its factorization.

261171604655981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 21772800, while the sum is 62.

The spelling of 261171604655981 in words is "two hundred sixty-one trillion, one hundred seventy-one billion, six hundred four million, six hundred fifty-five thousand, nine hundred eighty-one".