261509 has 2 divisors, whose sum is σ = 261510. Its totient is φ = 261508.

The previous prime is 261467. The next prime is 261523. The reversal of 261509 is 905162.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 136900 + 124609 = 370^2 + 353^2 .

It is a cyclic number.

It is not a de Polignac number, because 261509 - 2¹⁶ = 195973 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261529) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130754 + 130755.

It is an arithmetic number, because the mean of its divisors is an integer number (130755).

2²⁶¹⁵⁰⁹ is an apocalyptic number.

It is an amenable number.

261509 is a deficient number, since it is larger than the sum of its proper divisors (1).

261509 is an equidigital number, since it uses as much as digits as its factorization.

261509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 540, while the sum is 23.

The square root of 261509 is about 511.3795068244. The cubic root of 261509 is about 63.9482817856.

The spelling of 261509 in words is "two hundred sixty-one thousand, five hundred nine".