261565644421 has 2 divisors, whose sum is σ = 261565644422. Its totient is φ = 261565644420.

The previous prime is 261565644371. The next prime is 261565644523. The reversal of 261565644421 is 124446565162.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 181979028100 + 79586616321 = 426590^2 + 282111^2 .

It is a cyclic number.

It is not a de Polignac number, because 261565644421 - 2⁷ = 261565644293 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261565654421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130782822210 + 130782822211.

It is an arithmetic number, because the mean of its divisors is an integer number (130782822211).

Almost surely, 2^261565644421 is an apocalyptic number.

It is an amenable number.

261565644421 is a deficient number, since it is larger than the sum of its proper divisors (1).

261565644421 is an equidigital number, since it uses as much as digits as its factorization.

261565644421 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1382400, while the sum is 46.

The spelling of 261565644421 in words is "two hundred sixty-one billion, five hundred sixty-five million, six hundred forty-four thousand, four hundred twenty-one".