261721898917 has 2 divisors, whose sum is σ = 261721898918. Its totient is φ = 261721898916.

The previous prime is 261721898899. The next prime is 261721898939. The reversal of 261721898917 is 719898127162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 256738809636 + 4983089281 = 506694^2 + 70591^2 .

It is a cyclic number.

It is not a de Polignac number, because 261721898917 - 2¹⁵ = 261721866149 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261721898947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130860949458 + 130860949459.

It is an arithmetic number, because the mean of its divisors is an integer number (130860949459).

Almost surely, 2^261721898917 is an apocalyptic number.

It is an amenable number.

261721898917 is a deficient number, since it is larger than the sum of its proper divisors (1).

261721898917 is an equidigital number, since it uses as much as digits as its factorization.

261721898917 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6096384, while the sum is 61.

The spelling of 261721898917 in words is "two hundred sixty-one billion, seven hundred twenty-one million, eight hundred ninety-eight thousand, nine hundred seventeen".