781638 has 32 divisors (see below), whose sum is σ = 1838592. Its totient is φ = 218400.

The previous prime is 781633. The next prime is 781661. The reversal of 781638 is 836187.

It is a super-2 number, since 2×781638² = 1221915926088, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is an alternating number because its digits alternate between odd and even.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 781599 and 781608.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 781638.

It is not an unprimeable number, because it can be changed into a prime (781631) 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, 403 + ... + 1313.

It is an arithmetic number, because the mean of its divisors is an integer number (57456).

2⁷⁸¹⁶³⁸ is an apocalyptic number.

781638 is a gapful number since it is divisible by the number (78) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 781638, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (919296).

781638 is an abundant number, since it is smaller than the sum of its proper divisors (1056954).

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

781638 is a wasteful number, since it uses less digits than its factorization.

781638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 940.

The product of its digits is 8064, while the sum is 33.

The square root of 781638 is about 884.1029351835. The cubic root of 781638 is about 92.1160319210.

The spelling of 781638 in words is "seven hundred eighty-one thousand, six hundred thirty-eight".