781640 has 16 divisors (see below), whose sum is σ = 1758780. Its totient is φ = 312640.

The previous prime is 781633. The next prime is 781661. The reversal of 781640 is 46187.

It can be written as a sum of positive squares in 2 ways, for example, as 749956 + 31684 = 866^2 + 178^2 .

It is a super-2 number, since 2×781640² = 1221922179200, which contains 22 as substring.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 781640.

It is an unprimeable number.

781640 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9731 + ... + 9810.

2⁷⁸¹⁶⁴⁰ is an apocalyptic number.

It is an amenable number.

781640 is an abundant number, since it is smaller than the sum of its proper divisors (977140).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

781640 is a wasteful number, since it uses less digits than its factorization.

781640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19552 (or 19548 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 781640 is about 884.1040662727. The cubic root of 781640 is about 92.1161104876.

The spelling of 781640 in words is "seven hundred eighty-one thousand, six hundred forty".