261651821 has 2 divisors, whose sum is σ = 261651822. Its totient is φ = 261651820.

The previous prime is 261651799. The next prime is 261651829. The reversal of 261651821 is 128156162.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 137217796 + 124434025 = 11714^2 + 11155^2 .

It is a cyclic number.

It is not a de Polignac number, because 261651821 - 2⁶ = 261651757 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (261651829) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130825910 + 130825911.

It is an arithmetic number, because the mean of its divisors is an integer number (130825911).

Almost surely, 2^261651821 is an apocalyptic number.

It is an amenable number.

261651821 is a deficient number, since it is larger than the sum of its proper divisors (1).

261651821 is an equidigital number, since it uses as much as digits as its factorization.

261651821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5760, while the sum is 32.

The square root of 261651821 is about 16175.6551953854. The cubic root of 261651821 is about 639.5992127718.

The spelling of 261651821 in words is "two hundred sixty-one million, six hundred fifty-one thousand, eight hundred twenty-one".