261663509 has 2 divisors, whose sum is σ = 261663510. Its totient is φ = 261663508.

The previous prime is 261663499. The next prime is 261663533. The reversal of 261663509 is 905366162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 222099409 + 39564100 = 14903^2 + 6290^2 .

It is a cyclic number.

It is not a de Polignac number, because 261663509 - 2²⁰ = 260614933 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 (261663539) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130831754 + 130831755.

It is an arithmetic number, because the mean of its divisors is an integer number (130831755).

Almost surely, 2^261663509 is an apocalyptic number.

It is an amenable number.

261663509 is a deficient number, since it is larger than the sum of its proper divisors (1).

261663509 is an equidigital number, since it uses as much as digits as its factorization.

261663509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 58320, while the sum is 38.

The square root of 261663509 is about 16176.0164750163. The cubic root of 261663509 is about 639.6087362730.

The spelling of 261663509 in words is "two hundred sixty-one million, six hundred sixty-three thousand, five hundred nine".