261655021 has 2 divisors, whose sum is σ = 261655022. Its totient is φ = 261655020.

The previous prime is 261655019. The next prime is 261655073. The reversal of 261655021 is 120556162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 140896900 + 120758121 = 11870^2 + 10989^2 .

It is a cyclic number.

It is not a de Polignac number, because 261655021 - 2¹ = 261655019 is a prime.

Together with 261655019, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261655321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130827510 + 130827511.

It is an arithmetic number, because the mean of its divisors is an integer number (130827511).

Almost surely, 2^261655021 is an apocalyptic number.

It is an amenable number.

261655021 is a deficient number, since it is larger than the sum of its proper divisors (1).

261655021 is an equidigital number, since it uses as much as digits as its factorization.

261655021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3600, while the sum is 28.

The square root of 261655021 is about 16175.7541091598. The cubic root of 261655021 is about 639.6018201925.

The spelling of 261655021 in words is "two hundred sixty-one million, six hundred fifty-five thousand, twenty-one".