7840 has 36 divisors (see below), whose sum is σ = 21546. Its totient is φ = 2688.
The previous prime is 7829. The next prime is 7841. The reversal of 7840 is 487.
It is a happy number.
7840 is nontrivially palindromic in base 3.
It can be written as a sum of positive squares in only one way, i.e., 7056 + 784 = 84^2 + 28^2 .
It is a super-2 number, since 2×78402 = 122931200, which contains 22 as substring.
It is not an unprimeable number, because it can be changed into a prime (7841) by changing a digit.
7840 is an untouchable number, because it is not equal to the sum of proper divisors of any number.
It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1117 + ... + 1123.
7840 is a gapful number since it is divisible by the number (70) formed by its first and last digit.
It is an amenable number.
It is a practical number, because each smaller number is the sum of distinct divisors of 7840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (10773).
7840 is an abundant number, since it is smaller than the sum of its proper divisors (13706).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
7840 is a wasteful number, since it uses less digits than its factorization.
7840 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 29 (or 14 counting only the distinct ones).
The product of its (nonzero) digits is 224, while the sum is 19.
The square root of 7840 is about 88.5437744847. The cubic root of 7840 is about 19.8657677676.
The spelling of 7840 in words is "seven thousand, eight hundred forty".
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