261635021 has 2 divisors, whose sum is σ = 261635022. Its totient is φ = 261635020.

The previous prime is 261634987. The next prime is 261635089. The reversal of 261635021 is 120536162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 259660996 + 1974025 = 16114^2 + 1405^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261635021 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261635821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130817510 + 130817511.

It is an arithmetic number, because the mean of its divisors is an integer number (130817511).

Almost surely, 2^261635021 is an apocalyptic number.

It is an amenable number.

261635021 is a deficient number, since it is larger than the sum of its proper divisors (1).

261635021 is an equidigital number, since it uses as much as digits as its factorization.

261635021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2160, while the sum is 26.

The square root of 261635021 is about 16175.1358881463. The cubic root of 261635021 is about 639.5855234642.

The spelling of 261635021 in words is "two hundred sixty-one million, six hundred thirty-five thousand, twenty-one".