781731661 has 2 divisors, whose sum is σ = 781731662. Its totient is φ = 781731660.

The previous prime is 781731631. The next prime is 781731667. The reversal of 781731661 is 166137187.

781731661 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., 762809161 + 18922500 = 27619^2 + 4350^2 .

It is an emirp because it is prime and its reverse (166137187) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 781731661 - 2¹³ = 781723469 is a prime.

It is a super-2 number, since 2×781731661² = 1222208779619637842, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (781731667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 390865830 + 390865831.

It is an arithmetic number, because the mean of its divisors is an integer number (390865831).

Almost surely, 2^781731661 is an apocalyptic number.

It is an amenable number.

781731661 is a deficient number, since it is larger than the sum of its proper divisors (1).

781731661 is an equidigital number, since it uses as much as digits as its factorization.

781731661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 42336, while the sum is 40.

The square root of 781731661 is about 27959.4646050313. The cubic root of 781731661 is about 921.1971109006.

The spelling of 781731661 in words is "seven hundred eighty-one million, seven hundred thirty-one thousand, six hundred sixty-one".