261515921 has 2 divisors, whose sum is σ = 261515922. Its totient is φ = 261515920.

The previous prime is 261515897. The next prime is 261515923. The reversal of 261515921 is 129515162.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 259854400 + 1661521 = 16120^2 + 1289^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261515921 is a prime.

Together with 261515923, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (261515923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130757960 + 130757961.

It is an arithmetic number, because the mean of its divisors is an integer number (130757961).

Almost surely, 2^261515921 is an apocalyptic number.

It is an amenable number.

261515921 is a deficient number, since it is larger than the sum of its proper divisors (1).

261515921 is an equidigital number, since it uses as much as digits as its factorization.

261515921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5400, while the sum is 32.

The square root of 261515921 is about 16171.4538925849. The cubic root of 261515921 is about 639.4884592447.

The spelling of 261515921 in words is "two hundred sixty-one million, five hundred fifteen thousand, nine hundred twenty-one".