261555221 has 2 divisors, whose sum is σ = 261555222. Its totient is φ = 261555220.

The previous prime is 261555199. The next prime is 261555269. The reversal of 261555221 is 122555162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 151536100 + 110019121 = 12310^2 + 10489^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-261555221 is a prime.

It is a super-2 number, since 2×261555221² = 136822267264717682, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261555271) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130777610 + 130777611.

It is an arithmetic number, because the mean of its divisors is an integer number (130777611).

Almost surely, 2^261555221 is an apocalyptic number.

It is an amenable number.

261555221 is a deficient number, since it is larger than the sum of its proper divisors (1).

261555221 is an equidigital number, since it uses as much as digits as its factorization.

261555221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6000, while the sum is 29.

The square root of 261555221 is about 16172.6689510421. The cubic root of 261555221 is about 639.5204912494.

The spelling of 261555221 in words is "two hundred sixty-one million, five hundred fifty-five thousand, two hundred twenty-one".