781378009 has 2 divisors, whose sum is σ = 781378010. Its totient is φ = 781378008.

The previous prime is 781377991. The next prime is 781378043. The reversal of 781378009 is 900873187.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 596336400 + 185041609 = 24420^2 + 13603^2 .

It is a cyclic number.

It is not a de Polignac number, because 781378009 - 2⁹ = 781377497 is a prime.

It is a super-2 number, since 2×781378009² = 1221103185897608162, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (781388009) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 390689004 + 390689005.

It is an arithmetic number, because the mean of its divisors is an integer number (390689005).

Almost surely, 2^781378009 is an apocalyptic number.

It is an amenable number.

781378009 is a deficient number, since it is larger than the sum of its proper divisors (1).

781378009 is an equidigital number, since it uses as much as digits as its factorization.

781378009 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 84672, while the sum is 43.

The square root of 781378009 is about 27953.1395195602. The cubic root of 781378009 is about 921.0581747597.

The spelling of 781378009 in words is "seven hundred eighty-one million, three hundred seventy-eight thousand, nine".