41

Number
$41$ (forty-one) is:


 * The $13$th prime number, after $2$, $3$, $5$, $7$, $11$, $13$, $17$, $19$, $23$, $29$, $31$, $37$


 * The $1$st of the $6$th pair of twin primes, with $43$


 * The $7$th Sophie Germain prime after $2$, $3$, $5$, $11$, $23$, $29$:
 * $2 \times 41 + 1 = 83$, which is prime.


 * The $5$th of the sequence of $n$ such that $p_n \# - 1$, where $p_n \#$ denotes primorial of $n$, is prime:
 * $3$, $5$, $11$, $13$, $41$


 * The $6$th and largest lucky numbers of Euler after $2$, $3$, $5$, $11$, $17$:
 * $n^2 + n + 41$ is prime for $0 \le n < 39$.


 * The $1$st prime number which is not the difference between a power of $2$ and a power of $3$.


 * The $6$th integer after $7$, $13$, $19$, $35$, $38$ the decimal representation of whose square can be split into two parts which are each themselves square:
 * $41^2 = 1681$; $16 = 4^2$, $81 = 9^2$


 * The $4$th integer after $2$, $5$, $17$ at which the prime number race between primes of the form $4 n + 1$ and $4 n - 1$ are tied.


 * The $7$th integer $m$ after $1$, $2$, $3$, $11$, $27$, $37$ such that $m! + 1$ is prime

Also see

 * Smallest Prime Number not Difference between Power of 2 and Power of 3