16

Number
$16$ (sixteen) is:


 * $2^4$


 * The $1$st power of $16$ after the zeroth $1$:
 * $16 = 16^1$


 * The $1$st square number to be the sum of two triangular numbers in two different ways:
 * $16 = 10 + 6 = 15 + 1$


 * The $2$nd fourth power after $1$:
 * $16 = 2 \times 2 \times 2 \times 2$


 * The $2$nd power of $4$ after $(1)$, $4$:
 * $16 = 4^2$


 * The number of different binary operations that can be applied to a set with $2$ elements


 * The smallest positive integer which can be expressed as the sum of $2$ distinct lucky numbers in $3$ different ways:
 * $16 = 1 + 15 = 3 + 13 = 7 + 9$


 * The $4$th square number after $1$, $4$, $9$:
 * $16 = 4 \times 4$


 * The $4$th power of $2$ after $(1)$, $2$, $4$, $8$:
 * $16 = 2^4$


 * The $4$th square after $1$, $4$, $9$ which has no more than $2$ distinct digits and does not end in $0$:
 * $16 = 4^2$


 * The $5$th almost perfect number after $1$, $2$, $4$, $8$:
 * $\map {\sigma_1} {16} = 31 = 2 \times 16 - 1$


 * The $5$th powerful number after $1$, $4$, $8$, $9$


 * The $6$th of $35$ integers less than $91$ to which $91$ itself is a Fermat pseudoprime:
 * $3$, $4$, $9$, $10$, $12$, $16$, $\ldots$


 * The $8$th even number after $2$, $4$, $6$, $8$, $10$, $12$, $14$ which cannot be expressed as the sum of $2$ composite odd numbers.


 * The $9$th highly abundant number after $1$, $2$, $3$, $4$, $6$, $8$, $10$, $12$:
 * $\map {\sigma_1} {16} = 31$


 * The $9$th Ulam number after $1$, $2$, $3$, $4$, $6$, $8$, $11$, $13$:
 * $16 = 3 + 13$


 * The $11$th after $1$, $2$, $4$, $5$, $6$, $8$, $9$, $12$, $13$, $15$ of the $24$ positive integers which cannot be expressed as the sum of distinct non-pythagorean primes.


 * The $11$th positive integer after $2$, $3$, $4$, $7$, $8$, $9$, $10$, $11$, $14$, $15$ which cannot be expressed as the sum of distinct pentagonal numbers.


 * The $12$th after $1$, $2$, $3$, $4$, $5$, $6$, $7$, $8$, $10$, $12$, $14$ of $21$ integers which can be represented as the sum of two primes in the maximum number of ways


 * The $14$th integer $n$ after $0$, $1$, $2$, $3$, $4$, $5$, $6$, $7$, $8$, $9$, $13$, $14$, $15$ such that $2^n$ contains no zero in its decimal representation:
 * $2^{16} = 65 \, 536$

Also see

 * Definition:Hexadecimal Notation