781664 has 24 divisors (see below), whose sum is σ = 1658160. Its totient is φ = 360576.

The previous prime is 781661. The next prime is 781673. The reversal of 781664 is 466187.

It is a super-2 number, since 2×781664² = 1221997217792, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a self number, because there is not a number n which added to its sum of digits gives 781664.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (781661) by changing a digit.

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, 524 + ... + 1355.

It is an arithmetic number, because the mean of its divisors is an integer number (69090).

2⁷⁸¹⁶⁶⁴ is an apocalyptic number.

It is an amenable number.

781664 is an abundant number, since it is smaller than the sum of its proper divisors (876496).

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

781664 is a wasteful number, since it uses less digits than its factorization.

781664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1902 (or 1894 counting only the distinct ones).

The product of its digits is 8064, while the sum is 32.

The square root of 781664 is about 884.1176392313. The cubic root of 781664 is about 92.1170532763.

The spelling of 781664 in words is "seven hundred eighty-one thousand, six hundred sixty-four".