665781401 has 2 divisors, whose sum is σ = 665781402. Its totient is φ = 665781400.

The previous prime is 665781379. The next prime is 665781409. The reversal of 665781401 is 104187566.

665781401 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 581967376 + 83814025 = 24124^2 + 9155^2 .

It is a cyclic number.

It is not a de Polignac number, because 665781401 - 2¹⁰ = 665780377 is a prime.

It is not a weakly prime, because it can be changed into another prime (665781409) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332890700 + 332890701.

It is an arithmetic number, because the mean of its divisors is an integer number (332890701).

Almost surely, 2^665781401 is an apocalyptic number.

It is an amenable number.

665781401 is a deficient number, since it is larger than the sum of its proper divisors (1).

665781401 is an equidigital number, since it uses as much as digits as its factorization.

665781401 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 40320, while the sum is 38.

The square root of 665781401 is about 25802.7401839417. The cubic root of 665781401 is about 873.1936180584.

The spelling of 665781401 in words is "six hundred sixty-five million, seven hundred eighty-one thousand, four hundred one".