261405509 has 2 divisors, whose sum is σ = 261405510. Its totient is φ = 261405508.

The previous prime is 261405479. The next prime is 261405559. The reversal of 261405509 is 905504162.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 134212225 + 127193284 = 11585^2 + 11278^2 .

It is a cyclic number.

It is not a de Polignac number, because 261405509 - 2⁸ = 261405253 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 (261405559) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130702754 + 130702755.

It is an arithmetic number, because the mean of its divisors is an integer number (130702755).

Almost surely, 2^261405509 is an apocalyptic number.

It is an amenable number.

261405509 is a deficient number, since it is larger than the sum of its proper divisors (1).

261405509 is an equidigital number, since it uses as much as digits as its factorization.

261405509 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 10800, while the sum is 32.

The square root of 261405509 is about 16168.0397389418. The cubic root of 261405509 is about 639.3984492514.

The spelling of 261405509 in words is "two hundred sixty-one million, four hundred five thousand, five hundred nine".