261553921 has 2 divisors, whose sum is σ = 261553922. Its totient is φ = 261553920.

The previous prime is 261553889. The next prime is 261553931. The reversal of 261553921 is 129355162.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 261145600 + 408321 = 16160^2 + 639^2 .

It is a cyclic number.

It is not a de Polignac number, because 261553921 - 2⁵ = 261553889 is a prime.

It is not a weakly prime, because it can be changed into another prime (261553931) 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, 130776960 + 130776961.

It is an arithmetic number, because the mean of its divisors is an integer number (130776961).

Almost surely, 2^261553921 is an apocalyptic number.

It is an amenable number.

261553921 is a deficient number, since it is larger than the sum of its proper divisors (1).

261553921 is an equidigital number, since it uses as much as digits as its factorization.

261553921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 16200, while the sum is 34.

The square root of 261553921 is about 16172.6287597286. The cubic root of 261553921 is about 639.5194317179.

The spelling of 261553921 in words is "two hundred sixty-one million, five hundred fifty-three thousand, nine hundred twenty-one".