261005821 has 2 divisors, whose sum is σ = 261005822. Its totient is φ = 261005820.

The previous prime is 261005779. The next prime is 261005837. The reversal of 261005821 is 128500162.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 229522500 + 31483321 = 15150^2 + 5611^2 .

It is a cyclic number.

It is not a de Polignac number, because 261005821 - 2⁹ = 261005309 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261005621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130502910 + 130502911.

It is an arithmetic number, because the mean of its divisors is an integer number (130502911).

Almost surely, 2^261005821 is an apocalyptic number.

It is an amenable number.

261005821 is a deficient number, since it is larger than the sum of its proper divisors (1).

261005821 is an equidigital number, since it uses as much as digits as its factorization.

261005821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 960, while the sum is 25.

The square root of 261005821 is about 16155.6745758263. The cubic root of 261005821 is about 639.0724037788.

Adding to 261005821 its reverse (128500162), we get a palindrome (389505983).

The spelling of 261005821 in words is "two hundred sixty-one million, five thousand, eight hundred twenty-one".