781371991 has 2 divisors, whose sum is σ = 781371992. Its totient is φ = 781371990.

The previous prime is 781371977. The next prime is 781372051. The reversal of 781371991 is 199173187.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 781371991 - 2⁷ = 781371863 is a prime.

It is a super-2 number, since 2×781371991² = 1221084376638608162, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (781371931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 390685995 + 390685996.

It is an arithmetic number, because the mean of its divisors is an integer number (390685996).

Almost surely, 2^781371991 is an apocalyptic number.

781371991 is a deficient number, since it is larger than the sum of its proper divisors (1).

781371991 is an equidigital number, since it uses as much as digits as its factorization.

781371991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 95256, while the sum is 46.

The square root of 781371991 is about 27953.0318749147. The cubic root of 781371991 is about 921.0558101584.

The spelling of 781371991 in words is "seven hundred eighty-one million, three hundred seventy-one thousand, nine hundred ninety-one".