781718661 has 16 divisors (see below), whose sum is σ = 1195461120. Its totient is φ = 504334080.

The previous prime is 781718657. The next prime is 781718683. The reversal of 781718661 is 166817187.

It is a happy number.

It is not a de Polignac number, because 781718661 - 2² = 781718657 is a prime.

It is a super-2 number, since 2×781718661² = 1222168129911265842, which contains 22 as substring.

It is a Smith number, since the sum of its digits (45) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (781718621) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 466140 + ... + 467813.

It is an arithmetic number, because the mean of its divisors is an integer number (74716320).

Almost surely, 2^781718661 is an apocalyptic number.

It is an amenable number.

781718661 is a deficient number, since it is larger than the sum of its proper divisors (413742459).

781718661 is a wasteful number, since it uses less digits than its factorization.

781718661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 933993 (or 933987 counting only the distinct ones).

The product of its digits is 112896, while the sum is 45.

The square root of 781718661 is about 27959.2321246489. The cubic root of 781718661 is about 921.1920044472.

The spelling of 781718661 in words is "seven hundred eighty-one million, seven hundred eighteen thousand, six hundred sixty-one".