261783521 has 2 divisors, whose sum is σ = 261783522. Its totient is φ = 261783520.

The previous prime is 261783517. The next prime is 261783523. The reversal of 261783521 is 125387162.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 227677921 + 34105600 = 15089^2 + 5840^2 .

It is a cyclic number.

It is not a de Polignac number, because 261783521 - 2² = 261783517 is a prime.

It is a super-2 number, since 2×261783521² = 137061223734314882, which contains 22 as substring.

Together with 261783523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (261783523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 130891760 + 130891761.

It is an arithmetic number, because the mean of its divisors is an integer number (130891761).

Almost surely, 2^261783521 is an apocalyptic number.

It is an amenable number.

261783521 is a deficient number, since it is larger than the sum of its proper divisors (1).

261783521 is an equidigital number, since it uses as much as digits as its factorization.

261783521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 20160, while the sum is 35.

The square root of 261783521 is about 16179.7256157204. The cubic root of 261783521 is about 639.7065068684.

The spelling of 261783521 in words is "two hundred sixty-one million, seven hundred eighty-three thousand, five hundred twenty-one".