• 7 can be written using four 4's:

• There are 7 tetrahexes:

7 has 2 divisors, whose sum is σ = 8. Its totient is φ = 6.

The previous prime is 5. The next prime is 11.

It is a happy number.

7 is nontrivially palindromic in base 2 and base 6.

It is a Cunningham number, because it is equal to 2^{3}-1.

7 is an esthetic number in base 3, base 5 and base 7, because in such bases its adjacent digits differ by 1.

It is a weak prime.

It is a sliding number, since 7 = 2 + 5 and 1/2 + 1/5 = 0.7.

It is a cyclic number.

It is not a de Polignac number, because 7 - 2^{1} = 5 is a prime.

Together with 5, it forms a pair of twin primes.

It is a Chen prime.

It is a Harshad number since it is a multiple of its sum of digits (7).

It is a super Niven number, because it is divisible the sum of any subset of its (nonzero) digits.

It is a nude number because it is divisible by every one of its digits and also a Zuckerman number because it is divisible by the product of its digits.

7 is an idoneal number.

It is a tribonacci number.

It is a Lucas number.

It is (trivially) a d-powerful number and an alternating number.

It is the 3-rd Hogben number.

It is a pancake number, because a pancake can be divided into 7 parts by 3 straight cuts.

It is a Carol number, being equal to (2^{2} - 1)^{2} - 2.

It is a Kynea number, being equal to (2^{1} + 1)^{2} - 2.

It is one of the 548 Lynch-Bell numbers.

It is the 7-th Perrin number.

It is a partition number, being equal to the number of ways a set of 5 identical objects can be partitioned into subset.

7 is a lucky number.

7 is a nontrivial repdigit in base 2 and base 6.

It is a plaindrome in base 2, base 4, base 5 and base 6.

It is a nialpdrome in base 2, base 3, base 6 and base 7.

It is a zygodrome in base 2 and base 6.

It is a self number, because there is not a number *n* which added to its sum of digits gives 7.

It is a congruent number.

It is a panconsummate number.

Being equal to 2×2^{2}-1, it is a Woodall number.

It is a nontrivial repunit in base 2.

It is a pernicious number, because its binary representation contains a prime number (3) of ones.

It is a Pierpont prime, being equal to 2^{1} ⋅ 3^{1} + 1.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3 + 4.

It is an arithmetic number, because the mean of its divisors is an integer number (4).

It is a (trivial) narcissistic number.

7 is the 2-nd heptagonal number.

7 is the 2-nd hex number.

7 is a deficient number, since it is larger than the sum of its proper divisors (1).

7 is an equidigital number, since it uses as much as digits as its factorization.

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

The product of its digits is 7, while the sum is 7.

The square root of 7 is about 2.6457513111. The cubic root of 7 is about 1.9129311828.

The spelling of 7 in words is "seven", and thus it is an aban number, an iban number, an oban number, and an uban number.

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